Thanks to all for the replies. So to summarize mu understanding, surfskis originally looked like waveskis:
"This 1919 picture establishes
Harry McLaren as the first
maker of surf skis. "
Getting longer they kept their names ans while waveskis appeared in the 70ies, they had to take this name because the name surfski was already taken. I still think it's a pity the 2 names are not switched.