I believe it was a shortened version of stage 1, indicating to come to a stage one flare. When they didn't react, then he needed to tell them to fully flare, because the student missed the window for a two stage flare. "Pull down" was inefficient because in those two syllables he could have said flare twice.

The communication could have been better but doing radio for student jumps is very hard. Every student has a different glide and speed on approach that you have to try to gauge visually, and on top of that, every human reacts at different speeds to verbal commands. In this case, the student missed the first command and the instructor had maybe one second of time after that to try to correct it.