DCA final approach has unusually late and steep turns due to airspace restrIctions. I bet it ends up being a factor. The chopper pilot requested visual separation and saw the CRJ. From that point he must have been disoriented.
Always flown into IAD vs DCA ( when travelling - not a pilot lol ) so im not even familiar with the approach.
But from looking at the playback on FlightRadar24, there are a LOT of choppers and light aircraft in/around DCA at given times. Several chopper routes have them hugging the right bank of Potomac. This one seeming veered off that right bank toward middle of river.
Im guessing there will be even more restrictions now after this.