When I was in Catalonia, they said that this container and way of drinking are both local customs.

They explained it's a heritage from times of plague - this way you drink without touching (thus contaminating) it.

Heh. I'm guessing "normal" alternatives wouldn't clearly illustrate that it was a liquid that was being consumed.

The 'bota' (boot) is a leather/skin bag filled with wine that's very common in Spain. It's basically used the same way.