Definitely hacks. I also was once invaded by someone that dropped an insane number of runes and just left. I would throw them away imo, you wouldn't want to win by cheating.

Yup, hacks. I havent had this happen in Elden Ring, but I remember in some of the Dark Souls games people would do this kind of stuff. As a general rule never accept weapons or equipment from them because those could also be hacked and having them on your character could result in catching a ban from multiplayer. I feel like there was some other weird thing that would royally fuck your character up if you picked it up too, but I can’t remember the details