Because in some states in the US, not only is it legal to merge into a bike lane in preparation for a right-hand turn, it's actually REQUIRED. As has been mentioned, such is the case in California.
If you're turning right and there is a bike lane to the right of the travel lane, you are required to merge into the bike lane before the turn. In essence, the bike lane also functions as a turn lane.
So really it depends on the law in that location. The motorist may very well have had right-of-way, or may even have been required to merge into the bike lane in preparation for a right-hand turn.