Block Party Etiquette

I've lived in a middle class Suffolk town all my life (52). For the last 5 years, I've had a friend as a housemate. He's more outgoing than I, and sometimes makes people uncomfortable with his open nature. Admittedly, though, there are a lot of people that like his friendliness. Today, though, we had a disagreement. There was a block party about 5 blocks from us. We don't know anyone on that block. I said you can't go to a block party unless invited by someone on the block, it's not like the church feast. He insists block parties are all open season, since they happen on public streets. For clarity, my block isn't a block party block, and I've never gone to one unless invited by someone I know, even when it was 1 block away.