When the device is set for flipped, the document says:
Reported d-pad directions are flipped when in Upside Down mode — RIGHT will be reported as LEFT, UP as DOWN, etc. — so that the d-pad will make sense to a user holding Playdate upside-down. However, the A and B buttons — since they are still labeled as "A" and "B" — retain their normal meanings and will be reported as usual.
I'd like to recommend that the A and B buttons should be reported as "∀" and "ꓭ" in this case.