The 500' rule certainly applies to microlights, and up until recently they weren't allowed to fly over built up areas at all, even if they could glide clear. I believe this has changed and the same rules apply as for light aircraft, but some microlights may still have the restriction?
Apart from the bits at the beginning where there is a small village, it seems to mostly be over a deserted beach, there is maybe one person on the beach so he is probably breaking the law at times in this video, but largely not.
However, microlights aren't the quietest thing ever, I know they are quieter than a typical light aircraft, but it's a higher pitch tone which can be quite a nuisance to the locals. I hope he didn't annoy anyone with this type of flying, as it gives us all a bad name, I try to be as considerate as possible with my low flying. Looks like he chose a very deserted area though, so I'm sure there won't have been any complaints.