The tournaments are a separate area (and IIRC, business entity) from the restaurant, however the Gift Cards credit are stored on are available for use at both. It's pretty similar to having events at a hotel that happens to have a bar, there's still a physical separator of the two areas. You can't go about bringing booze into the game store area.

I don't think WOTC seems to mind that much, as employees frequent these legacy events too.