First of all, what the hell does this advice have to do with anything? How does his insecurity about his height relate to him having to learn about sex? How will learning about sex help him with his insecurity about his height. The issue isn't getting girls attracted to him; most likely there are already plenty of girls who are. The issue is helping him to realise that his height is a non issue so he can stop getting in his own way.

Secondly, what makes you think that watching porn will make him better at sex? Sure you might pick up a few techniques, ideas and so on, but porn is a stylised acted scene designed to look good, not necessarily be good. A lot of positions used in porn (including the ways guys normally give head in porn) are done that way simply to allow for cameras to get a good view of it. Then there's direction, takes and retakes, lighting crews etc. Trying to get good at sex by watching porn is like trying to learn to fight by watching Jean Claude Van Damme movies.
Telling someone that watching a bunch of porn will make girls want to fuck them just might be the worst advice I've ever heard on here. I mean, stop and think about what you just said.