Well, two things here:
First of all, the USAAF pilots had not encountered the IAR80/81 before and the misidentification can be understandable, as the Germans only had one radial-engined fighter in service.
Secondly, thinking that they were Fw190s would have them engaging the IAR80/81s using known traits and weaknesses of the Focke-Wulf, which the IAR did not possess.