i think it was more a case of Sam being impatient. there was no need to throw the ball to Kupp on his first pick. Just as there was no need to throw it to Arroyo or to JSN on two of the other three. Nor was there anything in the read of those plays that said he should do so... necessarily.
However...
I think what the Rams know about Sam and that other teams will begin to replicate, is that he is VERY reliant on the design of a given play and if he sees something that tells him off the bat that it will work, unless he has 5 seconds to reconsider, he may just lock on and toss one to you. And i understand why - he grew up in failed systms that stunted his maturation as a player and resulted in poor habits. Over the last two years, he has been in superior systems that do a good bit of the work for him (which they should). But he has become a bit too reliant on the play design doing the work for him, on working through the fundamental requirements of his position and not yet fully comprehending how the results of his actions should dictate what he does next.
Take the Arroyo INT. When he starts the play and looks left to diagnose coverage on that side of the field, he should be doing so to legitimately see if thats where he should go with the ball AND if he knows he wants to go to Arroyo, to see if that action moves the LB to the left or if he stays in place. If that LB doesnt move, he SHOULD consider another read, especially if there is pressure. He should ONLY throw to Arroyo if he gets by the LB (or if the LB moves left following his eyes) and has open field in front of him on his seam route. In this case, The LB doesnt move (Tell 1 in the read), he turns and runs with Arroyo in perfect coverage (Tell 2 in the read), and there is a Safety over Arroyo in the pattern (Tell 3 in the read). And despite all of those things telling Sam quite clearly he SHOULDNT throw there, he did anyway. He took the entirety of his time in the pocket to stare down Arroyo and throw the ball despite nothing telling him to do so.
If pressure was too fast, literally the thing to do is go away from that route because it takes too long to develop. Pressure only gets worse the longer you are waiting for a play to develop (i Hope Russ is reading this) and Kubiak gave Sam an out and a faster read.
The exact same thing can be said of the first INT except here, the coverage read on Kupp said throwing there was the correct INITIAL read. IF pressure is getting to him, he shouldnt simply stand static in place and wait for the play to develop. He should either take the outlet or scramble to buy himself time. That isnt a difficult, high level thing to do. It doesnt require 'PERFECT' play response, just fundamental reaction. And on that play, if Sam was REALLY understanding in its entirety what the DBs responses meant, he would have seen that the Safety over JSN abandoned his responsibility in coverage and left JSN open on the deep route. Instead, Sam took 3.5 seconds to do only one thing - stare down Kupp. He didnt consider that the the Safety would have time to come all the way across the field to pick of his ball nor did he see him doing so apparently.
These are just two terrible plays by the QB and have nothing to do with pressure forcing a bad decision. And i think they are indicative of a player trusting his first read too much when his clock gets interrupted and just letting it rip. Its like Sam requires 3.5 seconds on a play to avoid mistakes. Before SUnday, the line has given him an inordinate amount of time to go through his reads and allow plays to develop, hence his league leading YPC. The two things go hand in hand. But the criticism of Sam before he hot here was that he was less adept at the quick pass, quick decision game and i think that is 100% what we saw Sunday - A qb EXPECTING to have the time he needs to do what HE wants and not taking what the play says he should do.
INT to Kupp, he had 3.5 seconds and it still wasnt enough to get the pass he wanted off from where he chose to throw but did it anyway. But the shortened time to throw didnt prompt him to look elsewhere, he did what he wanted.
INT to JSN - he was pressured right away, rushing the throw but that didnt change his process, he wanted to go to JSN and did so regarldess of what was happening.
INT to Arroyo - he had ample time to read the play and make a better decision, but he inexplicably threw to the guy requiring the most protection and was 100% covered from the beginning to end - ie Arroyo shouldnt have been the read after about .5 seconds into his drop.