I am that friend, and let me explain my thought process. The idea is Randall being blown up to this size via the scream machine he was planning to use in kids to extract screams directly since in the film its implied thst excessive use of the machine on an individual will sorta drain them of energy like how Fungus is white and wheezing, so I figured dthe opposite of that would be someone like that conniving skinny little bastard getting extremely obese from kids screams (or laughter, which would probably get Jim to blob size considering kid laughter is much higher in energy level than screams)
and if I could add an idea, there's this newspaper that advertises a massive weight gain diet full of disgusting junky slop, with a picture of that exact magazine in the film. I'd think for some reason as a sort of revenge Randall is forced to undergo this diet and becomes immensely huge; It's not as detailed as the scream machine but if it's easier to draw I wouldn't mind