Hi Kilian,
It's not a dumb question at all. It's quite remarkable, but it was fairly common for German fighter pilots to utilize captured Allied aircraft - almost always suitably re-marked with German insignia - in combat. In addition, the two-seater airmen of Fl. Abt. (A) 208 flew a captured Breguet 14 B2 on reconnaissance missions. The Bulgarians had an Armstrong-Whitworth FK 3 (IIRC) that was re-marked in Iron Crosses, but I don't know if they used it on operational flights.
Just off the top of my head, here are some other examples of fighter pilots:
Eduard von Schleich famously used a captured SPAD VII, and was shelled badly by German flak.
Otto Kissenberth of Jasta 23b flew a Sopwith Camel in combat, and was put out of the war when he was injured in a crash.
Otto Bernert had a Sopwith Pup when he commanded
Jasta Boelcke, but I don't know if he flew it operationally or not. Later on Jasta Boelcke had both a captured Sopwith Camel and a SPAD for the pilots to test-fly, but I don't think they ever used them operationally.
Rudolf Windisch, in Jasta 32b, shot down and captured the SPAD VII of Capt. Oscar Monteiro Torres (from Portugal) of SPA 65. He is
reported to have flown it in
French markings on combat flights. After the urgent warnings of his comrades he painted it over in red, with Iron Cross insignia but retained the escadrille marking of SPA 65, and continued to fly it. He was later reportedly "banned" from flying this SPAD by higher authority, and went back to flying an Albatros D.V. Rammjaeger can tell you more about this, as he is the ultimate authority on Windisch.
Udet had a SPAD VII that he used as a runabout, a personal transport machine, but I don't believe he ever flew it in combat.
When he flew Rumplers with Fl. Abt. 7,
Paul Bäumer repaired a captured British Nieuport and flew it as a personal aircraft - but not operationally.
One can only wonder about the consequences if any of these pilots had come down in Allied territory flying a captured machine. They didn't bring their pilots much luck, for Leffers was (apparently) killed when flying his captured Nieuport, Pfeiffer of Jasta 9 was fatally injured in the crash of a Nieuport, and Kissenberth was severely injured in his Camel.
In addition, Jastaschule I and II both had examples of captured Bitish and French aircraft, but these were not flown operationally.
I'm sure there are others that I can't remember right now.
Greg