I don't think the dashcam footage helps much, if at all - you do appear to moving to the left as you start to go, but I guess that's a natural consequence as you turn slightly left to join the roundabout.
The other vehicle hasn't gone far enough for his intention to be conclusive so he could say anything.
There's a very similar junction that we use a lot where the left lane is very tight. You do see people in the middle lane drift left as they look right while creeping forward waiting for a gap to join the roundabout.