Скачать или смотреть Cyclists, Can You Explain This Fall?

This fall happened a while ago while cycling in Sicily, and to this day I can’t fully explain why it happened. No contact, no obvious hazard — yet I went down. Watch closely and let me know what you think caused it.

I had a pretty bad scratch on my knee, and a couple of bruises... there was a bit of blood but luckily it cannot be seen clearly on the video otherwise some squeamish viewers could be unhappy and YouTube could take send me a warning.
Personally I cannot explain the fall... but probably due to bad maintenance of the bike...
I assume back wheel went out of place and me with sandals could not keep balance or my foot on the pedals.