1. People can be jerks and sense your vulnerability and say the craziest things to watch you squirm. Especially if you seem cowering and quiet or they just want to dominate you and make you feel like junk. Some people get off on power and making other people a pariah and shattering their confidence.
2. I'm betting some of this could be brought on by your appearance, anxiety and how you carry yourself. Some people just aren't that great looking or have a voice or manner that is unusual and since folks can't put you in a box they gotta label you something crazy.
3. You remind them of someone that was really a pedo, and that's not your fault.
4. They are a pedo and need to label other people a pedo because inside they think someone might read pedo vibes off of them. Some of the most normal seeming people are really pedos. Mr All American frat boy stud could be trying to pick up 12 year olds online while at the same time trying to pick up the hot sorority sisters at the bar or having a serious girlfriend.

Bottom line the people saying this stuff are bullies. They may literally think what they said or not, its all about power and dominance over you. Not worth your time, but sometimes you have to get along with people like that in a school or work situation and it would be nice to get them off your back. Also, you have to watch your back around these people because you can't trust them. Protect your electronic assets and don't ever allow the possibility of them accessing your phone or other stuff because some of these jerks will set people up because they think its funny to set up a person they consider a freak or weird.

I think Richard Feynman's had it right when he thought it was stupid that people cared what others thought of them but unfortunately we live in a world where it matters in order to get and maintain a job, stay out of trouble, find and keep friends and a significant other.