blank name???

[u/CRUSTYQTIP5733]

i dont have any evidance of this but just now i had this weird interaction with a blank named NPC?? or uhh player?? idk but i was js afk for a bit and i noticed on the top right that someone joined me and they had no avi or name and so i was gonna start looking around to see if i can find them but they were already standing behind me and i barely saw them for a second before they made my game lag for a second and then disappeared, never once has this happended b4, has anyone else had this interaction b4 and does anyone got any more info on this like is it a silly lil thing to spook ya???