So the name stuck. It isn't really much different than calling them "radio buttons" even though they have nothing to do with radios.
[0] https://docs.microsoft.com/en-us/windows/win32/controls/abou...
The button set on the face of many dashboard radios would physically pop out the previously pressed button when you pushed a different one in so only one in the set would be selected. The name is pretty obvious if you've used the physical version but I haven't seen one since the 90s.
Similarly comboboxes are called like that because of historical reference (to the combobox control on Win32 that provided the functionality) even though they aren't really a combination of input box and list.
(though one could claim that they are still a combination of a button and a drop-down list, so the name still has some relevance to what is displayed, unlike radio buttons)
They work like radio buttons. How’s that having ‘nothing’ to do with radios?