I'll be honest with you, I always find it funny how people treat P-bot like a 5 year old with how they shame everyone for making P-bot even just a slight bit horny that day.
P-bot is a machine that randomly pick 4 highly-rated games and animations, and it tries it's best to avoid A ranked submissions. It's a slot machine of the good, bad, and the horny content people upvoted yesterday, and It's practically just reflecting people's tastes they had. So it says more about Newgrounds users themselves that they're trying to hide their own horniness from the "all-seeing eyes of P-bot"
And really why does all this hate even exist? You don't "win" anything for being picked by P-bot. At most you get a bit more views from being picked by P-bot, a pretty little trophy beside your post, and a bit of "fame" for 1 day. Getting front-pages are more valuable anyways because they're hand-picked by the team, it's out there for longer, and you get a lot more recognition. Meanwhile getting picked by P-bot is like winning a lottery, but with more steps. Actually no, it's much more like the stock market.
Again, so what if P-bot got horny today? You still have the other picks to go through, P-bot tends to remove A rated content pretty quickly, a new batch of picks will come tomorrow, and there's still the rest of the front page to explore. Why the big fuss? It's not like underage kids are going to accidentally watch the A rated content, you need a NG account to do that, and to the kids that are cheating their age, so be it. Let-em have their fun for a bit. I'm pretty sure everyone has done that before at some point right?
 It's just easier for them to defacto rate pieces A even if by all rights and rules those pieces are M or even lower. They just don't want to be harrassed about it. Let's be honest about what that is: successful bullying.
As for this, you don't know how this artist works. Everyone's got their own way of organizing their art. If you look at their page you can see they like to post their comic panels as individual submissions instead of using the new gallery feature. Maybe to them they prefer to just have a flat rating across that comic series. Though, one thing I found humorous is their image version of this animated comic didn't get an A rating on any of their submissions.
Could it be true that this artist got harassed in the past? Probably. However, you can't just go with what comes to mind immediately without asking the artist in question first. Maybe the artist legit has no idea how to rate some of their posts, and can't decide which rating would best suit their work, so they flip-flop between an A rating and an M rating.
Again, Occam's razor's a bitch if you just assume everything.
In the end I'll leave you with this: I have a Civilian rank, you have Scout rank, and the third guy has a Sherif rank. Think of that what you will.