"luckysystems" keeps joining my server

This guy named "luckysystems" keeps joining my world from time to time even tho we have a whitelist on, and it's only 2 of my friends and me. I'm confused if he wants something from us or idk, cuz what? Also, why does this happen? Who is this guy, and why does he keep joining from time to time? I think he joined over 4 times in the span of like a week
https://imgur.com/t1MwVoG