Computer crashes after typing μ in chat

Me and my friend were playing together in an aternos server, adn after doing something weird trying to access the /gamerule randomTickSpeed command, he deleted everything he had typed and he pressed enter. When he did this the letter μ appeared in chat my framerate dropped to about 1fps and his monitor shut off. My pc crashed and had to restart. When i tried to recreate the issue by just typing μ in chat, nothing happened.