Listen, I got two choices there:
1. Switch out and keep Altaria for later on
or
2. Keep it in and get KO'd by your Shadow Ball
And don't come with " Altaria's faster with 2 DD's", it was paralyzed. Yours where faster. The only smart choice were to switch to Milotic and see what happens.
I ws just saying you won because you got lucky. Nothing else. I would've won otherwise.