"The point that I’m trying to make is if you’re going to spent months of your time and thousands of your dollars drafting a concept, hiring a team, and building a free and completely open source video game as a hobby, you better use zombies as your theme."
That is not the right thing to have learned from this. I suggest this one:
If you're going to take a bunch of ideas and content wholesale from a community for your new thing, it might be good if you engage with that community and make something that respects the context of the stuff you're taking, instead of making something they'll perceive as cheap and foreign.
Which community would that be? 4chan? Reddit? The rest of the internet that also regurgitates memes?
You cannot 'engage with' the internet as a whole. No community owns a meme: it's the fact that so many people reproduce them that makes it a meme. The problem here is that some folks do feel they, or their community, own a meme. These people are the problem, not this guy with a place for a game. Or at least, he's another kind of problem.
The engaging with the community isn't so that you can make a petition that says, "Are you cool with my game [Y/N]" and have everyone on the Internet sign it. It's so that you can create something which demonstrates an awareness of the culture and doesn't come off as derivative and shallow to the people who deal in it daily and care to defend it.
If he had made a post on Reddit or talked to anyone on 4chan and said "I want to make a meme-themed iOS game, help me make it not suck" and listened, he probably would have wound up making something that did not entice people to mock him and insult him. That's what I mean about engaging.
That is not the right thing to have learned from this. I suggest this one:
If you're going to take a bunch of ideas and content wholesale from a community for your new thing, it might be good if you engage with that community and make something that respects the context of the stuff you're taking, instead of making something they'll perceive as cheap and foreign.