The seller isn't necessarily being weird, "sofa-cum-bed"/"sofa-come-bed"/"sofa-co-bed" is actually how people refer to it in some places.

https://www.urbanladder.com/blog/5-types-of-sofa-cum-bed-that-every-home-needs

I think it comes from the Latin for "with". The same thing happens with some historical academic distinctions

https://en.wikipedia.org/wiki/Latin_honors

summa cum laude (/ˈsuːmə/), meaning "with highest praise", typically awarded to graduates in the top 1%, 2%, or 5% of their class, depending on the institution. Some institutions either do not award the summa cum laude distinction or award it only in extraordinary circumstances

J. D. Vance was honored as sofa cum bed in college. They won't let me add that to his Wikipedia for some reason.

He graduated sofa cum bed. Top of his class.

No lowballers! I know what I got!

This is reminding me of my favorite tank ammunition, The penetration-cum-blast round

Meet me at the cum bed. 👉👈

LOL That’s some !WildMarketplace@sh.itjust.works

Does it come pre-loaded or you have to fill it up yourself?

JD is that you?

Sofá cama