I would think that any aircraft would be so novel to them, and the range of WWII aircraft so similar, even from a Yak-3 to a B-29, that they would be all treated much the same. The whole concept of a flying machine or boat or ship or mechanical bird, however it would be perceived, would seem like some kind of magic.
In a military sense, they would soon learn they would be safe from machine guns if they could get under heavy stone roofs, and that only deep caves and excavations would protect them from most bombers.
Here's a thought. You're on the Iron Throne in the world of A Song of Ice and Fire. Would your reaction really be any different if the Red Tower was strafed by BF-109s vs being strafed by P-51s? I don't think so. Now, imagine a bombing run. How would you react differently to the Red Tower being targeted by a dozen JU-88s vs. a similar number of B-24s? I think that if you survived, you would learn very quickly that towers weren't a good place to be when the "giant magic bird machines" were flying, and I doubt you would be counting engines and declaring, "Oh, no worries, they're only light bombers" before a run.