Yeah, I watched that one too. His stance and movement are not typical of pure Muay Thai.
As far as early defenses against that clinch...
You know how you're always saying that a low stance is a good defense against takedowns? Look at how high you are in the moment when he enters on you.
While you're at it, look at the relative positions of your feet. At the moment before the entry, he had stepped out with his right foot to your 10 o'clock while your feet were still pointing straight forward with your left foot forward. That was already exposing your left flank. When you threw the overhand left swing, that gave him the spot under your left armpit on a silver platter. Adjusting your feet before swinging would have helped you. Also remember that throwing an overhand swing with your lead hand is an open invitation to a wrestler unless you set it up just right.
As far as starting your own pre-emptive grappling technique which could break an arm - are you talking about attacking the left arm that he was using to stiff arm you in the face while setting up his shot? If so, your feet were in a poor place to do so. You'd need to fix your stance first.
I'd kick with whichever leg allows me to target the back of your leg. So if you're standing in a side horse stance with your right leg forward, I'd be kicking with my left leg. First option is to kick your leg as you plant it after a kick. Second option is to lead with a flurry of punches and end the combination with the leg kick as you cover or retreat.