Added speed

I was throwing with a mate of mine and when we started pitching (he’s also a pitcher) he told me to “squash and point” mean with the high leg lift and over the top action that i have, squash my leg into my chest and when releasing point where u want it to go.
I tried this on the mound and to my suprise i gained 3-4 mph on my fastball, now throwing about 84-86 and a 12-6 break on my curve (instead of the sluve that i usually have). I realise it has something to do with momentum towards the plate, but why such a big difference?

Can’t be certain without seeing your old and new mechanics. But my guess is the verbal cues your friend gave you caused you to do something that improved your mechanics and/or your timing. As a guess, maybe tucking your knee to your chest caused you to keep you leg in the air longer resulting in a longer stride and more momentum while staying closed a bit longer.