It might be that a lot of people misuse "passive aggressive" as a synonym for "indirect". I.e., leaving a note for your roommate is not inherently passive aggressive. It could be from conflicting schedules, being intimidated by confrontation, whatever. PA is when someone says "gee, I sure wish someone would do the dishes" or just not doing dishes themselves to make you mad and punish you with fruit flies to force you to do them. PA is about using passivity in place of aggression.

I've gotten accused of being passive aggressive for being polite, too. I think it was just a perspective thing. I'm not a confrontational person, and I have this whole etiquette persona, and some people think I'm being insincere or facetious. American culture (probably other places, but I can't speak for them) (also, I'm pretty sure I remember you being USian, so sorry if I got that wrong) doesn't value public etiquette in the same way it used to. These days, people don't generally care as long as you're not outright rude. Which is fine, but it leads to etiquette-focused people being snooty/PA/etc. Sorry, went on a bit of a rant there.

So, yeah, I don't think your coworkers are necessarily passive aggressive. They might be, but I think it's more that direct people don't always see indirectness as and equal quality, and vice versa.