Villain Donks River for Pot on dry board

Def one of the strangest plays I've seen at 5NL thus far. I'm pretty much never folding in this spot but admittedly, I did think it over since I was expecting him to just check fold smaller pairs, busted draws, or check call 9x, TT/JJ. This was another "everything is super standard until the river lolz"

He donks for POT on said river on an absolute brick. I suppose I could have jammed the rest but it completely threw me off. He never has 22. Slowplayed 99 or 66 is possible but I think he goes for a value raise on the turn at the very least. I don't know if he 3 bets K9 pf.

So what, in your opinion, does he do this with? Our hand is very under repped, and lately, I've been mixing in calls with AKo specifically. Does his range from SB contain weaker Kx? Can he take this line with A9 of diamonds? I think if he was going to pot it, he may as well just ship for maximum fold equity. If he shoves I probably tank but still call cuz i'm a donk lol.

NL Holdem 0.05(BB)
UTG ($4.37) [VPIP: 20% | PFR: 8.6% | AGG: 25% | Hands: 37]
HJ ($5.40) [VPIP: 25% | PFR: 10% | AGG: 33.3% | Hands: 21]
CO ($6.18) [VPIP: 19.4% | PFR: 17.9% | AGG: 50% | Hands: 69]
HERO ($5.38) [VPIP: 22.1% | PFR: 18% | AGG: 27.5% | Flop Agg: 38.9% | Turn Agg: 28.9% | River Agg: 12.5% | 3Bet: 8.4% | 4Bet: 26.1% | Hands: 1215]
SB ($6.42) [VPIP: 23.3% | PFR: 20% | AGG: 42.9% | Flop Agg: 66.7% | Turn Agg: 0% | River Agg: 50% | 3Bet: 33.3% | Fold to 3Bet: 0% | 4Bet: 0% | Hands: 31]
BB ($5.07) [VPIP: 17.6% | PFR: 17.6% | AGG: 0% | Hands: 17]

Dealt to Hero: K♠ A♦

UTG Folds, HJ Folds, CO Folds, HERO Raises To $0.17, SB Raises To $0.46, BB Folds, HERO Calls $0.29

Hero SPR on Flop: [5.07 effective]
Flop ($0.97): 6♦ 9♠ K♣
SB Bets $0.31 (Rem. Stack: $5.65), HERO Calls $0.31 (Rem. Stack: $4.61)

Turn ($1.59): 6♦ 9♠ K♣ K♦
SB Checks, HERO Bets $0.51 (Rem. Stack: $4.10), SB Calls $0.51 (Rem. Stack: $5.14)

River ($2.61): 6♦ 9♠ K♣ K♦ 2♥
SB Bets $2.48 (Rem. Stack: $2.66), HERO Calls $2.48 (Rem. Stack: $1.62)