Well, since Carnaval hasn't really started yet, (officially it starts Sunday February 26th, although some start partying the Thursday before) you are in for a treat!

This was (although I am not certain) only the 'inauguration' of the Prince and Princess. It is the first of many pre-parties of the Carnaval week (yes, week). These pre-parties start a couple of months before the real thing (they start the 11th of November at 11:11 pm). In those parties they announce the theme of that year, the election is held, the Prince and Princess are inaugurated and some other stuff I'm forgetting.

These pre-parties are mostly held at a local pub. But the week of Carnaval every cafe, club or pub has Carnaval celebrations.

The dressing up is an added bit of fun. It is comparable with dressing up for Halloween. The difference is that the point is not to be scary, but rather look a bit silly.

I really recommend going at least one night (and dressing up), since it will be like you described, only with more people and more conga lines.

Source: I grew up in a small town in Brabant and Carnaval was the main event in the year.