You can sort of see what he is thinking in imagination there.
What Youngblood is talking about side step and hook you can see him practicing more at 1:18 to 1:25.
I dont know what 'check hook' means really ; id be thinking glove goes up to the side of the head checking a long shot, roll with it slip under as the your same blocking arm drops down and goes back around the outside of his extended arm as you adjust stance and hook, Even better; double hook, check slip one low hook, step in adjust into one high hook just as his arm lowers to the reaction of the first hook.

Funny but if you step off his center line and into his rear arm still facing him then throw a rear hook of your own it goes right through the path of his lead arm if he threw it in reaction to you going in there. That would be a real check hook, block with the outside of the arm while the hook lands. You'd be working right in the hole though and using center line tactics and choking out his rear arm with your lead glove and fighting the other arm with your rear at the same time for it to be safe.