The Gilliam in the film is an imposter, a fraud, and most of all a traitor in willfully leading his followers to their doom. It's not a redeeming feature that he obviously believes in Malthusian democide just like his supposed nemesis Wilford that, as we find out in the end, he actually works for. Bong went and gave the character Terry's name and Terry's looks, so it's not too much of a stretch to perceive it as a hostile comment on Terry's non-conformist, counter-culture rebel attitude and us, his loyal fans. If there'd been a friendly motivation behind it, Bong would admit to it, but in interviews he even openly denies that the character is named after Terry, denies that he gave him Terry's looks, and denies that Terry's films have had any influence on any of his films, especially this one, when clumsily trying to rip off "Brazil" is in fact written all over "Snowpiercer".
I wouldn't mind even if Bong had had more talent and would've been better at imitating Terry's style, but his choice of incorporating a character in the film that's not there in the original comic that's most blatantly based on Terry and whose characterization and behavior as a villain and traitor in the context of the film looks like a hostile attack on Terry IRL certainly doesn't seem just like a friendly nod. And on top of it, after basically offending Terry and not portraying him in a good light, he's even so dishonest about it that in interviews he denies having done it at all and dismisses Terry's films as not that influential or notable overall.
I wouldn't mind even if Bong had had more talent and would've been better at imitating Terry's style, but his choice of incorporating a character in the film that's not there in the original comic that's most blatantly based on Terry and whose characterization and behavior as a villain and traitor in the context of the film looks like a hostile attack on Terry IRL certainly doesn't seem just like a friendly nod. And on top of it, after basically offending Terry and not portraying him in a good light, he's even so dishonest about it that in interviews he denies having done it at all and dismisses Terry's films as not that influential or notable overall.