Form looked pretty good, but it's hard to watch these sideways.
I watched the video before reading your post. My first thought, "his weight is too far forward, his heals are coming up." Try and focus in keeping the weight on your heals more.
As for the soreness, it may just be due to squatting more. Do you have a foam roller? If so use it. If not, roll a tennis ball around on your hip, also try lying on it and rolling over it. This should hurt. Also warm up more with things like leg swings, step-ups, whatever. Also maybe add in a couple more quick warm ups, keep them light.
Last thing that really works for me is using a mini band to do leg abducton (forcing your legs open... think the good girl/bad girl machine, but with a band)
Good luck with Smolov Jr. I like it as a quick stimulus program to get you used to more volume.