Well I stated it a couple times but maybe I wasn't clear enough.
The question broadly put to Brady is this: did Brady, or did he not, suffer concussions and conceal them from the team and/or the NFL?
By responding to that question at all, he raised the status of the question by drawing attention to it after it had been a back-burner issue for most of the offseason. This question and versions of this question and implications related to this question will now be asked of him more often.
By responding to that question without definitively denying that he'd suffered concussions and concealed them from the team, he created an impression that raises the status of the question still further -- the impression that he may have actually done this thing that potentially violates NFL rules (depending heavily on how you interpret those rules).
At this point a mediot with an agenda wouldn't even have to ask Brady further questions in order to allege that he did indeed conceal concussions from the NFL. Discussing the question without definitively denying the allegation makes it look like it's a thing he CAN'T deny. Which gives the media all the ammunition they need to keep harping on it all season.
And the best part is he really ought to have known that this was the kind of question that should have answered with silence. There isn't a player in the NFL that knows the wiles of the media and handles the school of sharks with microphones better than Brady, but this is an unfortunate lapse by him. By responding to this question without putting it to bed, he's created the media's Brady narrative for them for the entire 2017 season maybe even encouraged the Usual Suspects to start investigating him all over again. It's just a bad scene.
To review in short: He should not have said anything, and if he did say anything, he should not have said that..