Based on your description of the scenario I'd think the driver in question considered you a "queue jumper", and their fury at what they perceived as your objectionable driving would cause them to act unsafely.

I see similar things from time to time on a road I use frequently. In cases where it's very busy and both lanes fill up then merging in turn tends to happen quite well, but when there's only moderate traffic and it's queuing in one lane then events such as that you describe may occur. Perhaps some signs saying "queue in both lanes" and "merge in turn" at the appropriate points on the road might improve things.