In summary:
Bashur was talking to what he claims a 14 year old girl while he was 17, then he turned 18 and she turned 15. SkyDoesMinecraft claimed that Bashur told Sky that the girl was actually 13. Which one is telling the truth, who knows
Either way,
according to Bashur's own admission (start at 16:35) the girl's parents found out, a private investigator came to his house and this later led to him being arrested. He was successfully convicted but managed to avoid jailtime and was given court mandated therapy and apparently lost access to his electronics for awhile.
The people on Twitter are possibly referring to other allegations against Bashur like a girl who came forth saying Bashur was sending her thirsty messages when she was 17 and he was 28
Or they're just idiots who don't know Bashur himself admitted to talking to a 14 year old on the internet when he was nearly a adult