Not exactly the same situation as last time, but pretty close (with this board, a flush straight was possible, so it's not just one card that could beat me...) - I've got K-high flush on a 4-flush board where two people are definitely acting like they also got the flush. At least I didn't 3-bet this time, but I was still looking at cold-calling a raise on the river here.

Party Poker 0.15/0.30 Hold'em (10 handed)

Preflop: Hero is UTG+2 with , .
UTG calls, UTG+1 calls, Hero calls, 1 fold, MP2 calls, MP3 calls, CO calls, 1 fold, SB completes, BB checks.

Flop: (8 SB) , , (8 players)
SB checks, BB checks, UTG checks, UTG+1 checks, Hero checks, MP2 bets, MP3 folds, CO calls, SB calls, BB folds, UTG calls, UTG+1 calls, Hero calls.

Turn: (7 BB) (6 players)
SB checks, UTG checks, UTG+1 checks, Hero checks, MP2 bets, CO folds, SB calls, UTG calls, UTG+1 calls, Hero calls.

River: (12 BB) (5 players)
SB checks, UTG bets, UTG+1 raises, Hero calls, MP2 folds, SB folds, UTG calls.

Final Pot: 18 BB

Results in white below:
UTG has Qs Kh (flush, queen high).
UTG+1 has Kc 7s (flush, ten high).
Hero has Qd Ks (flush, king high).
Outcome: Hero wins 18 BB.

Was I wrong to cold-call the river here?

I think SSHE send some mixed messages about KQ offsuit.

Page 73:
Big Offsuit Broadway (AK, AQ, AJ, and KQ)
.......You can open with any of these hands from any position. Raise any of these hands if it has not alread been raised.(40)
.......If the raiser is very wild, sometimes raising with hands suck as K6s and 33, reraise with AJ and KQ as well.

(40) If the pot is already many-handed, perhaps fiver or six limpers, consider just limping with AJ and KQ. Your preflop edge is relatively small against so many opponents, and your call should give you strategic advantages which can make up for your small theoretical loss from not raising by allowing you to outplay your opponents after the flop.

Page 80:
Tight Games (3-5 players on Average to the Flop)

Chart:
Early Position

If there is no raise
Play: AA-77, any two suited cards ten or higher, AK-AJ, and KQ
Raise: AA-TT, AKs-AJs, and AK-AQ

Middle Position

Raise: AA-99, AKs-ATs, KQs-KJs, AK-AJ, and KQ

On page 73 they advocate raising from any position it seems, but the chart on page 80 says to play, but not raise, from EP.