why is this a thing?

i died to a Lucian and noticed damage without an icon, these are usually uncommon so i hovered over it and noticed what it said (after laughing hard has hell and telling my friends what it said of course) i'm curious to see why this is a thing or how it came to be. i didn't get a pic of the first time since i couldn't screenshot it but i died later and got a picture on my phone to prove it to my friends.