What was his problem?!

A first for me - got shouted at by a cyclist this morning and can't quite work out why!

I was waiting to go over Vauxhall bridge (northbound) in the bit where only buses and cycles are allowed. For non-Londoners, it's complicated, Vauxhall cross is a monster gyratory system but this bit in the middle means you can ride straight across to the bridge, which is 3 lanes inc 1 bus lane, turning into four lanes at the end (with a right only lane appearing).

So the lights go green and I pedal off, heading over to the right lane whereas the majority of cyclists peel off to the left for the bus lane. I go for the right because I turn right at the end of the bridge and there are enough lanes for cars to go around you, plus the phasing of the lights means I have a bit of time before the cars come.

This cyclist passes me on my right ultra close as we cross the junction, I jumped a bit because he was so close (he had obviously come up behind as the lights changed so he had a bit more speed) and he shouts something at me. He looked p*ssed off so I doubt it is a friendly Hello! Then he keeps looking back at me with an evil look his face, as though he expects something back but I did not hear what he said so I can't reply and then he veers left in front of me to get to the bus lane and I carry on, and he goes straight on while I go right at the end so that's the end of it.

What did I do? All I can think of is that he was 'assuming' I would veer left into the bus lane like 9 out of 10 cyclists do there, and thus 'assuming' he would have room to overtake me on the right as I did. When I did not and carried on towards the right lane, he was left with hardly any room due to the crossing kerbs that we had to ride between, and he got peed off and shouted at me.

Seriously, I would like to know what I did, motorists giving abuse is one thing but cyclists is another! I would have asked him if I caught him at the lights but they went green.