YouTube - Michael Jackson Tribute - Stockholm. July 8, 2009

wow thanks for that man!!do you know what's the story behind this?! did people just join in as they pleased or what?!?!

You're very welcome.
At first I thought they were a whole dance school or something like that. But then I read it's the swedish dance group, "Bounce" that were behind it (They are the first few people who start the dance). In the youtube describtion it says:

These are two performances made at Segels Torg and the Central Station (a third installment is planned to happen at Stureplan at 23.00 tonight).

The dance collective Bounce came up with the idea and invited the public to a short choreographed session before hitting the streets.

Here is the third video at Stureplan/Stockholm:

YouTube - Michael Jackson tribute the FINAL by night- stureplan Stockholm. July 8, 2009