Simply looking at the 'rankings' is a non-contextual view of how well (or not) Breno is pass protecting this season. You have to look closer, at the actual 'grade' and range of distribution, for a more accurate statistical view.
Based on these stats, Breno is currently grading out a very respectable 93% (92.8 to be exact) on pass block snaps, which ranks him 54th out of 65 eligible players. However, that grade actually rates him closer to the #1 rated player on the list (Joe Thomas, 97.8, difference of 5.0) than it does to the #65 player (Michael Harris, 87.4, difference of 5.4).
In more localized terms, comparing Breno to Russell Okung, the difference is 4.0. Which is to say that Breno is allowing 4 more pressures per 100 pass plays than Okung. 100 pass plays roughly equates to 3 full games based on the Seahawks' average volume of pass plays. 4 pressues over 3 games equals just over 1 pressure per game. (1.33) Thus, Breno Giacomini, who ranks #54, is only allowing slightly more than one additional pressure per game in pass protection than Russell Okung, who ranks #6.
So what does this tell us? It doesn't tell us that Breno is comparatively an elite NFL pass protector - he is not. But it does tell us that while Breno may rate statistically worse than the majority of starting OT's in the league in pass protection, he does not rate materially worse than virtually any of them, and isn't the liability in pass protection that this raw 'ranking' might suggest.