Unkillable bugs killable

[The Bonitaest Lissaest]

So yesterday while playing vanilla multiplayer with my husband shadowwalker1234 (his steam name) we were working on Skull Cavern together and I noticed he somehow was killing the red armored bugs in Skull Cavern. I tried and I was hitting for 0 but with his galaxy sword he was doing 100+ damage per hit and killing them in which they drop bug meat. He had no idea they were supposed to be unkillable until I said it. Clip of stream for proof: https://clips.twitch.tv/LovelyAwkwardSlothItsBoshyTime

The only thing that I can think of is we did do the item code naming exploit but we both did that and as you can see I can't kill them and he can.

[The Bonitaest Lissaest]

that link is supposed to say "Awkward Sloth Its Boshy Time" without the spaces. Flipping censoring

[LittleSadDragon]

Same. We have no mods or anything like this, just he can kill bugs and I can't