That anecdote is so typically Zen. It reminds me of some lines from the famous ‘contract scene’ [pictured below] from the Marx Brothers film A Night at the Opera. Groucho says to Chico, ‘Now just put your name right down there and then the deal is legal.’ Chico says, ‘I forgot to tell you. I can't write.’ Groucho says, ‘Well, that's all right, there's no ink in the pen anyhow.’ Those lines, like so many of the Brothers---especially those uttered by Groucho---are so Zenlike.
Back to the Zen story. Joshu commands the monk, who seeks truth, not to stay where the Buddha---a symbol of truth, meaning and purpose---is. Not only that, but Joshu commands the monk to pass quickly through any place where the Buddha is not. The monk is even commanded not to bring up (that is, mention or discuss) Buddhism to anyone. How seemingly very odd! Here we have two Buddhists who, one would have thought, have either found or (in the case of the monk) are seeking truth, meaning and purpose in life through Buddhism---which by the way is only a religion in some but by no means all of its manifestations---and along comes this learned Zen master who appears to be saying that we must look elsewhere for the truth.
Meaning and purpose in life is to be found in the living of your days---in the living of these days. Do not seek truth anywhere else. Indeed, do not seek it at all. Just experience it in all its fullness. And in order to do that you need only live mindfully---that is, with choiceless awareness of whatever is---from one moment to the next.