What techniques are being used here to influence the subject to pick a certain outcome?
Priming is a phenomenon where an exposure to a stimulus affect/influences response to another stimulus. It is however, a broad definition which may or may not fully explains what actually happened in the video.

For what's it worth, I notice that number 7 was the only number (between 0-9) that didn't appear at all in any of the arithmetic calculations, answers or questions. But I can't say that I understand how this could influence subject's choice.