From the information that is available so far, it appears the helicopter was flying along a charted helicopter route and was in contact with ATC, so they were under positive control. The charted helicopter route also requires the helicopter to be at or below 200 feet, unless otherwise authorized by ATC. The chart also says that helicopters should fly at the maximum permissible altitude if the ceiling allows, so it should have been at 200 feet (MSL). It is a good question if and why TCAS/ADS-B was possibly turned off, though.