Correct, thin and long needle (usually yellow) is pointing directly to the selected waypoint. It's a beeline to it but it's not necessarily the desired flightpath. In order to be on preplanned path longer needle should "sit" inside thicker (shorter one) one.
I haven't seen instruments video but I believe it's a course intercept he was reffering to. So if you're heading 90° on course to waypoint 1 and but your next waypoint is in 180° direction instead of flying directly over WP1 and overshooting desired flight path you'll intercept it from 4-5 km out. You simly switch to WP2 when 4km from WP1. Your thin needle (beeline) will automatically switch in WP2 direction and you'll notice it's pointing at cca 150° at your HSI which bring you on a 60° intercept by formula of beeline - current heading = intercept heading (150° - 90° = 60°).
Got it?
Not sure I understand this? Can you explain more?