My cat decided to barf all over his stuff

My cat throws up sometimes. took her to the vet and he said she must be over eating. So I feed her less now and she hasn’t thrown up in a very long time. My so fed her too much last night and then our friend came over. He brought his guitar and the case.

He gets up and uses our restroom and my cat takes the opportunity to go to the edge of the couch and barf right onto his guitar and case. I felt so bad, I cleaned it up for him and he was like “it’s okay, It’s not like you knew it would happen or can control it.”

But still just...