How do you mean?
On the other hand "emulator" is usually some hardware emulation. Whereas the flas player was basically a runtime / vm for Flash files. And Ruffle is a different runtime implementation.
It's like saying any non-oracle Java is a "Java emulator".
Scummvm for example follows that line of thought: "ScummVM is a complete rewrite of these games' executables and is not an emulator."
Anyway, given what Ruffle says I would probably side with them....