Is this considered hacking?

Well, I visited a site where u could vote...
Then, in an eager to win, I kept pressing Enter, resulting in heavy traffic and the site becoming very slow...

Later, it was announced as a hacker attack...
But, I'm really curious if this is considered hacking at all
Coz I've been to a lot of sites which allows u to vote as much as u want & nothing happen...
Furthermore, the site allows users to vote unlimitedly... So... Is this considered hacking?