Sorry in advance for long post-Just by seeing other threads on this and my own personal experience it seems to be that we've just gotten to the point of mistrusting anyone who gets out of a line regardless of the reason.
I feel like it's like the whole "have to be fair to everyone" speech: "If I do it for you then I have to do it for others". I think we rationalize what isn't a big deal and what isn't.
Just as an example I live in a suburb of Kansas City, KS and as the Royals had won the World Series we had a huge parade and rally in Downtown Kansas City, MO with the people in charge finally giving an estimate of 800,000 people in attendance.
Here's a pic of where most of the crowd was (and this isn't showing where all the people actually were):
Now my sister-in-law and I were sitting on a rock wall with other people in pretty much the heart of the most crowded area. A bottleneck near us had occurred and people were wanting to jump over the rock wall to get to the other side because the direction they were facing wasn't moving. In reality there was no where for those people to go to because everywhere was a crowd. However, this kind man was allowing a mother and child to climb over the rock wall where he was sitting on because they had their family on the other side in the deep mass of people waiting for them. Yeah....30 minutes later and people were still climbing over the rock wall only now they were pushing into us nearly knocking over a little girl next to me. We kept trying to cut them off for several hours from climbing over but it was mob mentality at that point. And to be honest it boiled down to one guy being nice to one family and everyone else saying "well hey he let them through why not us".
Moral of my story is while we would all like to be the really nice people sometimes there are reasons not to be. Is taking a child out of a queue to go to the bathroom as big of a deal as others joining up in line after they've gone and done other stuff? To most people no, but the issue is still the same people got out of a queue and want back in or others joining a queue. Both can create a negative experience to those around and many people on other threads have pointed out if you had to ask if it was wrong or if you did the right thing (when it comes to queue questions) you likely were in the wrong (though not all questions are of the same severity).
I'm not sure what prompted the guy to call out the OP but it could be that they had that happen to them the umpteeth time and was fed up with seeing it or it could be that they are THAT type of person. If we rarely saw people abusing the kindness of others (kindness meaning allowing a parent who had previously exited a queue to take a child to the restroom back into the queue) then there likely wouldn't be as much mistrust. Instead we see the parent situation mentioned above combined with family members off enjoying something else while only one person stands in line then when it's time the whole group joins the one person. and imagine that that family is not the only one to do so in the queue for that attraction so now we have a domino effect and now we have a mistrust of ANYONE getting out of a line regardless of the reason (and yes everyone does have a tolerance for what bother them and what doesn't).