I'm not 100% sure that they didn't know, and weren't just clout chasing.
I have a hunch that the "no longer associating with him" is just a PR stunt.
It's 50/50, depends a lot on how much digging they did first. Anyone doing cow-type commentary definitely knows Lucas' name will bring in a few views, but that's true of pretty much anyone who has even a little Internet notoriety.
If you listen to Lucas or just look at his recent (i.e. from 'right now right now right now' 2017 on), it's just a "rumor" that started when the alleged barista was 16 and that
technically isn't pedophilia. It's also true that he's never been charged or convicted of soliciting a minor so if they look up his legal records all they'd really find are the DV thing and a few trespassing citations, but nothing involving underaged girls.
If you don't do much digging on it and just go by Lucas' recent social media and the old articles about the Starbucks thing it's pretty easy to miss posts from 2013/2014 where he straight up said "I'm a straight pedophile who has never committed the act" and there are still a lot of people who believe that shit is photoshopped for one reason or another (partially why I made sure to include the Facebook URL in the screenshots), doubly so since those posts are friends only and if he's not your Facebook friend you can't find them at the source. They are still there, however, I have a burner that's friends with him and they show up if you search his profile for the word "pedophile".
Edit: So, if we're giving benefit of the doubt, and that person just thought the pedo shit was rumors or half truths, I can definitely see wanting absolutely nothing to do with him for the lols after finding out it's actually true. Those are less common screenshots to see when looking into Lucas; I've had a few people in live chats or in Discords ask me to send them those screenshots as they hadn't seen them before and wanted to take a look at them directly--and occasionally to repost them as they hadn't seen them before and thought Lucas was just a ridiculous overreacting incel, but not an actual pedophile.
Edit 2: And you know what? Just so they're recent again, here they are.
If you look at the date stamps, these are all really old posts and that's part of his defense against them now; he goes back and forth between "Well those are old" and "I was joking/my roommate posted those", yet he never goes back to delete them which is very, very telling.