AITA for not defending the honor of a fellow pooper?

Dear friends:

About a month ago, I was using the handicap stall at work, one of my favorite workplace activities. Things were proceeding normally, when I hear a knock on the stall door. "Are you almost done in there?" Clearly the man has a situation to deal with, and I do my best to accommodate, responding: "I'll just be a moment." and proceed with my normal sanitation routine. (I'll spare you all the details, but I'm sure you get the idea.) This isn't enough for our friend, who then begins a tirade: "You shouldn't be using the handicap stall. Do you want me to contact your manager? You know you can get fined $250 for using a handicapped stall without being handicapped? I will contact HR." This is obviously a bit off-putting, and I respond with "Give it a rest buddy, I'll be out in one moment." I finish washing my hands, and pop the stall door, give the guy a big smile. "She's all yours bud." and proceed out of the restroom.

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I return to my desk, and proceed to do a quick google. I first check if there is actually any legislation/fine associated with using a handicapped stall. There isn't. The only actual legislation revolves around size/dimensions/accessibility. I then google "handicap stall etiquette" - the internet's general consensus is that using a handicap stall is ok, especially if other stalls are occupied, and no handicapped people are actively waiting to use it. I'm pretty sure I'm in the clear, I have a laugh about it, tell the story to a few close friends, and go on with my life.

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Fast forward to today. I'm once again, as is my prerogative, getting paid to poo. This time I'm using the regular stall - I've avoided the handicapped stall for the most part since "The stall Nazi" incident. Some unfortunate soul did not get the memo, as I hear a knock at the stall door next to my own. "Are you almost done in there?" "There sure are a lot of handicapped people around here, I should start taking pictures and sending them to HR." I stifle a laugh, and maintain my silence. I immediately text my girl - "The stall Nazi strikes again!" and relay the story to her.

She calls me out for not defending the rights of the downtrodden, and allowing this guy to continue his reign of terror.

My stance is that:

1. I believe the sanctity and silence of a men's restroom should be maintained at all times, with the exception of fart and plopping noises.
2. I don't want to get involved with this guy, he's clearly a spaz.
3. I DEFINITELY don't want to get caught up in some HR incident, it's always been my policy to avoid interaction with HR, for reasons that should be totally obvious to anyone who has spent any time at all working in corporate America.

Am I an asshole for not getting involved?