2 minutes in, Paul types out [xfs] and then later [xtc] — what do you think these symbols are for?
My best guess from watching the video is that they are temporary place holders, breadcrumbs he leaves himself to return to, allowing him not to break his flow/train of thought. If that's the case, then the technique reminds me of Neil Strauss's "Power of the TK":
When you get suck on a word, or cant’ think of the right fact, what shouldn’t you do?
Don’t stop. Just type, TK.