Mike plays the double-five.
Hmmm, does that mean that he doesn't have any 4's? (in particular, the 4-3! Isn't he supposed to have a bunch of 3's? Well, there's the 6-3, which he doesn't have (he passed on 6's), and the 4-3. Now, given that he has the double-5 (he just played it) and that the 5 is a head, if he plays the 4-3, the 3 would also be a head, which means that he might be forcing someone to kill the double-five.
So that means that yes, maybe
he does have the 4-3 but he chose to play the double-5 to avoid keeping
a double that was going to be killed.