Not convinced hes betting KQ here and definitely not 78 imo.
OPs stats so far would be very relevant. He is not yet an established reg at the site in question and has less than 100bbs. Granted in villains shoes I probably check/fold weaker two pairs against a reg, against a <100bbs non-reg I don't think I could.
Also I think me coming up with that value range has detracted from just how many bluffs there can be here. Although granted I think I should have at least thrown some negation in to the KQ/78 hands I think there's no way we can give villain enough credit to check/fold these 100% of the time on the river as he certainly has them in his turn betting range always.
As for A7/AQ I don't think these would be particulary bad bets on the turn. AQ crushes flush draws loses less to KQ betting than it would check/calling and may have very few combos of weaker Kx to worry about depending on OPs current image. (I'd have about 6 here assuming there isn;t a fish in the blinds).
A7 is certainly a better c-bet than a check/call on the flop and on the turn gets the oppurtunity to fold out better made hands yet value town draws. Both are more likely to value bet the river than KQ and 78.
Not saying I'd make the bets myself but don't think they can be 100% ruled out.