He may be talking about this: https://www.sportsinjuryclinic.net/cybertherapist/front/knee/indexjumpersknee.html
or this: https://www.emedicine.com/EMERG/topic347.htm
The normal growth of a guy of 17 yrs. of age will get you the type of improvements you seem surprised by. You are still physically maturing, even without the weights. Your superior marks without the training could also suggest overtraining/improper rest periods/etc. from before. However, the lack of training at the time of your new bests likely means you won't be able to repeat those performances consistently (as a competition season demands). You'll be fine without the squats at this point. Athletes your age can certainly and have hit the marks you are looking for without the weights. I know athletes that have hit 47' and 23' at that age, and could jump out of the gym, by things like bounding, jumping around with a weight vest (basketball, etc), and by competing (at a time when they hadn't yet found the weightroom). Later, when you plateau with your marks and when the pain is gone, the squats may come in handy to break barriers. Yes a program can come in handy, but I'm thinking perhaps at times (esp. at a younger age and for those that haven't plateaued) it may be more beneficial to be less systematic and just 'jump around' in different settings and experiment with different workouts. Antigravitdocg's post really resonated with me. I've recently had instruction by a great coach that said he could get me 3 extra feet in the triple jump through bounding, salsa dancing, and a weight vest alone. There's something potent about having a deep understanding and feel for movement. He related to me seeing a guy try to long jump that could deep squat 700 lbs.+, but he applied the force in such a way that he shattered the take-off board and landed only a 5 meter jump. This past year, proper strength training, etc., as I learned it here took me and the jumpers I coach a long way toward where we wanted to be. On top of that, reconnecting with movements such as agentwinburn8604 points out, "using multijumps instead because of their sport specific and teaching nature in a natural way", may be the x-factor, the unknown factor which will top it all off, though logic may suggest is less than ideal. I am caught between two seemingly opposing schools of thought, perhaps like agentwinburn8604 is, and looking for a way to bridge the two. Just some rambling thoughts at 3:00 am. I've got a great respect for both worlds, but it has left me, too, a bit confused in my search for certainty.