In your game, you actually got a handicap of “1 stone”, which just means that you get to play as black with komi reduced to 0.5 points. This is the standard handicap for 1 rank difference, while receiving two stones is appropriate for 2 ranks difference.
Your opponent’s rank was displayed as 18k, however, their underlying rating number also has an associated uncertainty (“deviation”) that is particularly high, which indicates that their rank is not so reliable.
Normally, one would expect to see 4 handicap stones in a game between a 22k and 18k. However, it seems that @flovo and @anoek are suggesting that the high uncertainty in your opponent’s rank may have played a role in the system automatically reducing the handicap that you received for that particular game. Given the high uncertainty, the system appears to be assuming your opponent may actually be as weak as 21k, and possibly the handicapping system is using that conservative estimate.
Further, @anoek seems to suggest that the behavior of the system may require further consideration.