replace cyclist with tractor or farm vehicle. Would you be on here ranting?
You have set an expectation that, because the person is on a bike, they have an obligation to move over.
Yeah, maybe he could have moved over, but given you are in a car and cars are a pretty pish poor commnunication device, you couldn't have a quiet word with him to ask if he could move over, so let your anger seethe over.
You could have actually stopped yourself and taken a breather (the couple of minutes which markymark referred to) and calmed down. Indeed, given you were on a country track, that tells me you weren't in a rush, and if you were then you shouldn't be driving down single track roads and expect to make fast progress.
Life is too short buddy. Your progress is no more important than the cyclist pottering down a country lane or a farmer going about his business.