Are the Houthis like Hamas or something and he’s saying it’s wrong that anyone would support them?

Think about what this would look like during WW2. Would rooting for the Soviets to win the battle of Stalingrad make you a Stalinist or even a tankie? Of course it wouldn't - you are just cogniscent of the fact that things would actually get a whole lot worse if the Soviets lose. But that won't stop a whole bunch of fascists (and their liberal sympathizers) from pretending that you are. Not much has changed about that.

When someone is dropping bombs on your neighborhood and murdering people like you right in front of your eyes you don't get the luxury of waiting for a squeaky-clean and Hollywood-perfect organisation to hand out AKs and Semtex - you have to go with what is there. And a lot of what is there aren't the nicest of people because the nicer people either don't have the logistic support to give you anything or are simply dead. If the old PLO (Palestinian Liberation Organization - which was a lot more nationalistic than Hamas) was still around, these same liberals would be hysterically demonizing them in this scenario, too.

There’s a lot to learn to be a good leftist, imo!

Not much point in being a "good leftist" (whatever that may mean) in my opinion - I'd rather say be a "good at it" leftist.