I would bet dollars to donuts on this. Especially since it seems that the information about the aircraft circling was stepped on. When the controller asked if the helicopter had the original sight when the conflict alert went off, the helicopter reported it did. They saw an aircraft where they thought they’d see one.
I have 15 years of experience at a tower and I have probably have had over a couple dozen times where I noticed the pilot might have the wrong aircraft in sight (getting too close, cutting off the guy they are supposed to follow, etc). When I see this occur I restate where the aircraft is and ask if they have that one in sight.
For this situation the controller asked if the helicopter had the CRJ in sight. The pilot saw aircraft #2 on a straight in and assumed it was the CRJ. The whole situation could have been avoided had the controller simply said “off your left” when he asked. He did nothing wrong by not saying such and all indications from the helo told him the situation was managed. Tragic comedy of errors.