If I had to take a guess I'd say the inflation/popping thing is a hybrid of bdsm tenancies and either transformation fetish or balloon fetish. I honestly find it odd that he can't pinpoint what in childhood might have started that since most kink people I know or have read about have had very clear "aha!" moments about when that kind of thing gave them a boner first. It kind of points to either Dobs lying to his girlfriend about not knowing, or the thing having developed later in life after getting bored of normal porn and finding it online.
If we're honest most art fags draw porn of shit at some point for gratification. Rebecca Sugar, Steven Universe' creator, used to post Ed Edd N Eddy porn online. It's at the point that most people in the industry don't give a shit if you draw porn, as long as you are an adult about it and realize that shit doesn't really belong in an open critique meet or gallery. He would have been better of when caught in the Catty N thing to just go "ok you got me, I just wanted to keep that stuff out of my professional umbrella by using a pseudonym cause I know it's too weird for most people to want to see if they search me up." but his ego had him deny the whole thing and that just makes potential art directors skim right over you since you can't even be honest under pressure.