So it looks like he was hit then!!
I wouldn’t infer that – that’s an insurance broker site, they are only interested in “is there someone else we might be able to claim from” which usually means “single policy holder”!
I’ve only ever heard the police use single vehicle collision in the literal sense of one vehicle – ie, not looking for another driver. If they thought there was another vehicle involved their appeal for witness/dashcam would have described the second vehicle they wanted footage of.
Whilst the natural assumption when a cyclist is found in the road is that a car must be to blame, there’s plenty of people on here fallen off without a car being near them. An unlucky landing can be fatal. The state of the road surface those things will probably increase. It’s also possible it was a medical issue not a bike handling one that caused the problem.