I don't know any vegans personally (I've always lived in red states), so my experience with them comes from comments on food videos or blogs. It's like a school of fish or something, a whole huge group of them will suddenly target a channel and flood the comments with vegan propaganda, complaining that the recipe isn't vegan (despite the person not being vegan, so why would it be?), pushing their favorite vegan channel, and always using hundreds of emojis. So, yes, I think vegans are pushy and preachy, because that is how they behave online. There must be some nice, sane ones who are embarrassed by that and would never dream of lecturing their friends, but enough are like that in real life that the stereotype remains.