They definitely see it as an insult. Check the comment history and you’ll see there is no attempt at irony. Just an angry poster who’s fallen too deep into it.

If you go to very leftist areas of the internet (socialist or communist areas, anywhere from anarchistic (bottom left) to authoritarian (top left)) you'll see people using liberalism by its political science definition, rather than the definition its taken on within American culture. It stems from the idea of capital moving freely (that is, liberally) without restrictions. You'll also see it referred to as neoliberalism in the same spaces.

Full disclosure, I myself am pretty extremely socially libertarian (arguably borderline anarchistic), and have used liberal derogatively myself.