It was a successful delaying action. They were outnumbered hundreds to one and never expected to defeat the entire enemy army themselves. They knew they were going to lose that battle, but the intent was to help win the overall war, which the Greeks did.

And if you kill many more of the enemy than they do of you despite being vastly outnumbered, you can justifiably say you gave a lot more than you got, which is a victory of sorts in its own right.