This is just a hunch, but considering the ex-wife's behaviour (going out and hooking up with another guy) she has already given your friend Scriptural™ grounds for divorce, and Scriptural™ freedom to remarry.
Why she didn't get DFd herself is beyond comprehension - unless her "liason" was with a JW and now the two of them want to get married. So they have to turn the tables on your buddy, make him look like he's promiscuous (or not being very discrete at least) and DF him, in order for ex-wifey and her boinking-buddy to be eligible to be married in a Kingdom Hall.
There's always a howl of protest when a JW wants something that the rules of the religion prevents them from having. In turn, they have to manufacture and orchestrate situations that elevate them above those who are preventing their achieving what they want. The squeaky wheel gets greased, or at least in this case, lubricated in some manner.