It's a pop-culture reference to the title of a recent novel and play, which is, in turn, a Sherlock Holmes reference.

https://en.wikipedia.org/wiki/The_Curious_Incident_of_the_Do...

A common way to do this would be to take a branch with the male pollen-producing parts, and 'dust' the flowers on a female specimen with that. Doesn't seem far-fetched the ancients knew this helped to produce a rich harvest. And- from the article:

"As palm trees can be extremely high, this was a very perilous enterprise. Why did this worker even attempt this in a deserted garden will remain a mystery."

One possibility: some plants can be quite selective on when / under what conditions pollination is most likely to succeed.

Probably because fruit (+ seeds) follows, and a plant 'wants' those seeds to be distributed at the right time to maximize chance of offspring success.

Again: maybe such conditions were known, and gardener climbed the tree when the time was right. Which happened to be when no-one else was around.

Of course that's just 1 theory. Maybe gardener just didn't perceive it as dangerous.