Pretty easy for a 14y old with a photoshop license to fake. Just saying.
Normally I'd want to see the URL and see if it was spoofed. (If it was possibly spoofed, the next thing I do is check the FAQ. On a fake website, there are invariably some fairly hilarious mistakes with the English used in the FAQ.)
In this case, I was curious, so I went to the official Seahawks Pro Shop website. I looked through every jersey. There are #6 Diggs jerseys, but no #6 Mayfield jerseys. So I checked the ANY NAME jerseys, and that's where things got fun.
They used to have a function where you can punch in a name and number, and it would display the jersey with that name and number. I tried that with a blue jersey, and nothing happened. No display. Interesting. Then I tried it with a white jersey. That one did have the display function, so I typed in Mayfield with the number 6. It gave me the 6, but it only gave me MAY in the name tag. I retyped the name with "FIELD" included, but in doing so I misspelled the name as MAFIELD. It let me do that, and displayed it. I punched in the missing Y, and... nothing. The software simply would not let me put the name MAYFIELD in the name spot and display it for me, but it would let me display typos and spelling errors all day long.
Sooo... I'm guessing that someone put in Mayfield's name and the number 6 in a customizable jersey, then took a screenshot of that and posted it. And then the Seahawks shop responded by disabling the features that would display such a jersey again -- no customizable white jerseys using Mayfield's name, and no customizable blue jersey displays at all.
Funny stuff!