It’s not confusing at all… How is this any more confusing than:
Flatpak - they’re not literally flat…
Snap - I’ve never seen or heard any evidence of something snapping by any definition of the word I’m aware of.
Dolphin - what the fuck is this, no sea life whatsoever!
Kate - this is a text editor, not a person.
Distrobox - not in an actual box.
etc.
The main difference to your examples is that an “immutable OS” is in fact mutable, while none of your examples describe themselves with an adjective that is contradicting with their function/inner workings.
Flatpak is a pretty good name, because it makes software flat in the sense that it avoids having a (tall) dependency tree.
I installed Bottles, but was disappointed when it didn’t actually have anything to do with bottles.
If you think every name of every product, etc., is going to be literal… you’re gonna have a tough time in life.
Bottles is a noun and not an adjective.
Also bottles has no IT related meaning, while immutable does.
“Immutable OS” is not a product name.
An “immutable” OS becomes mutable whenever a user wants to change anything on it.
Now imagine I keep describing my car as undrivable, because it only becomes drivable when somebody gets in and drives it. - You’d think that this is a completely deranged statement.