I say this is a call. You have been called by the SB after opening UTG. So ranges from both players should be pretty tight. A decent player should not be calling wide from SB vs UTG and should not be opening wide UTG either.
Therefore I'd say villain is very unlikely to have a 7x hand. AA and KK would both 3bet pre-flop so that means 44 (3 combos), 77 (1 combo) and A7s (1 combo).
There is plenty of reason to think that villain may have tried to bluff you off the hand on the turn with a strong ace (AJ+) since the king is a pretty obvious 2nd barrel card.
There is also the possibility that they have a KJ/KQ type hand and after trying to get value from the turn now want to use the A
as a scare card to steal the pot
Call here and if they have you beat then make notes on what they had. If they had a set/boat then "good for them" it's a cooler, move on. If they turn up with K7o or 78s then you make a note saying they call super wide from SB vs UTG and pound on them for doing this later in the session. If they have complete air, make a note and keep making these calls (or raise them) when they bluff you in the future.