Well put two and two together and see where that takes you.
Unless you expect the guy to come out and admit it there isn't much we can do about it beside applying common sense.
Check it out yourself, try
insane seven (formerly known as Horny Family) and see if it doesn't ring any bells.
You can also hop into
harem island to see the resemblance in writing and artstyle.
So if you're like me, and you're not buying the "Hello, i'm a fresh new dev and i studied under Eroniverse for a while and now i'm ready to try my luck at game dev" and "i'm quitting because of bullies" then this should be enough.
Listen, i'm not trying to incriminate him or anything, i'm just simply trying to put these things out for some people here, who clearly can't seem wrap their heads around the fact that he is giving up under such a minor offense, especially since we never really witnessed any negativity aimed his way.