It's just a quarter, there is a thing called variance that causes results to be off from the mean if the sample size is small even when all factors and variables point to another expected outcome.
Besides variance, it could be because of substitutions. If you're the better team but your backups end up playing a lot in a quarter while your opponent has his starters in play, you can lose the quarter even though you're the better team overall. Again, it's caused by a small sample size, and in general, you cannot draw conclusions from small sample size.