Stealth Bomber does not have a capture flag, should not be able to be captured, I cannot say that it is not bugged.
According to "
Da Rules - Explained", the 'Capture' flag means that a unit is able to capture
other (capturable) units, not that it can be captured itself. In the epic-game .biq, all land-units with the AI-strategy(s) 'Offensive' or/and 'Defensive' (must) also have the 'Capture' flag.
Conversely, the
capturability of a 'normal' unit (i.e. not Hidden Nationality, or Leader, King, or Princess/Flag-units) depends on its A/D stats: any unit with D=0 (and A=0?) can be captured — in the epic game, Workers, Settlers, Scouts, Explorers, and bombardment-units — provided that the capturing Civ is already permitted to build that unit, e.g. Expansionist Civs can capture foreign Scouts/Explorers (but just for the sake of perversity, even though Hwach'a
cannot be captured by other Civs, once Wang knows Gunpowder, Korean units
can capture other Civs' Cannon!

)
Which also adds more evidence that the screenshot in the OP
is from a modded game: if the Jerk could capture Ottoman Stealth Bombers, then presumably he not only knew how to build them, but their D-value (and A-value?) must also have been set to zero here. (I can't remember: did Stealth Bombers also have D=0 in Vanilla?)
As to the huge size of the AI-army, I'm guessing that the Diplo/Space VCs were
also turned off for this game/mod — or it's being played beyond that win/loss notification.