Text in chat says '!/ found <username> and !/replace

i was playing on a world, when suddenly chat says '!/ found Lemonz23747 (my username) and !/replace (not replaceitem). it had no username, all it had where the username was meant to be was !/. i played on that world for about half an hour when that happened. unfortunately, i do not have a screenshot, as when that happened i instantly closed the game because i was freaked out. the world was in creative, was in the latest version, and i only used the /locate command to find a plains biome and a village.

also, i’m pretty sure the command /found <username> and /replace doesn’t exist.

 

the world file is attached, please check it out as soon as possible.

(this is my first bug report, i dont know if the world files help in any way)