Sorry, the vlo speed is actually 250 kts (Max speed at which gear can be extended).
So, in the haste of the situation in trying to decend rapidly and also slow down, maybe the pilot put the gear down earlier than usual at over 250 knots but the safety system had overridden the command. So despite the lever being down, the gear didn't extend and so the Landing gear alarm was sounding as per in the ATC communications. And so for some reason the pilot believed gear was down but it wasn't.
Pure speculation on my part but possible!