Ok, so this was something really weird that happened to me...

I was going to go to some random barrow and the nearest place I had discovered was Alftand

So I fast traveled there and walked north east towards the barrow, (might have been Saarthal actually) when a Blood dragon landed RIGHT in front of me.
I didn't hear it before it landed so is scared the crap out of me, so I took out my swords and were about to attack when I saw the dragon still standing there and looking at me like 4 feet away but it didn't attack. After a couple of seconds it flew away and started attacking random frost trolls and ice wolves, but still didn't attack me. It didn't even appear hostile on my compass

I wonder if this was like a rare random encounter or a bug, but it was after I completed the main quest so it might have something to do with that?

Probably a bug.

But to summarise: A blood dragon lands to eat a random traveller, realises its the Dragonborn, wets its pants realising this traveller is responsible for the near extermination(again) of its race, and promptly decides to eat a troll instead.

I would be walking around whistling the shaft theme song for the rest of the tamrielic day after that.

I had the same Blood Dragon stare at me and do nothing, and when I killed him I couldn't absorb his soul.

But that was ages ago.