Dorsett had 528 yards receiving in his second NFL season - Indy, 2016 - so 500+ yards this season doesn't seem at all unreasonable, especially now that he appears to be clearly "on the same page" with Brady.
There were signs of that late last year, though. Dorsett (without having experienced OTAs or Camp) was pretty poor in the first half of 2017, catching only 4 of 8 targets, so a lot of fans had written him off by the BYE week. After the BYE, however, he caught 8 of 10 for 109 yards, and went 2 of 3 for 50 more yards in the post-season. A catch rate of 77% on a ypc of 15.9 yards over the course of 9 games active isn't awful, especially considering the typical completion percentage on that depth of target for most QBs.
So, it's perhaps worth noting that, in his 2016 season in Indy, his ypc on 33 catches from Luck was 16.0 yards, with a catch rate of only 56% (up from 46% as a rookie). He ended last season with the Pats having a 67% catch rate on a 16.2 ypc. The 46% to 56% to 67% arc seems to show that Dorsett is capable of making steady improvement.
Yesterday's 100% catch rate (7-for-7 on a ypc of 9.4 yards) certainly isn't going to hold up (LOL!), although it begins to show that Dorsett can be very effective on shorter routes, in addition to deeper ones.
I wouldn't say that yesterday's "gameplan favored" Dorsett, particularly. From what I saw, Dorsett wasn't the first, or even second read in Brady's progression on about half of his targets. Brady appeared to be looking to Hogan before Dorsett most of the time, but the Texans' defense appeared to be more focused on taking Hogan away, too. So, the coverage almost certainly had more effect on the number of targets Dorsett saw, and on Hogan's 1-for-5 performance, than McD's gameplan.