Odrade:
After all, he was still so new to "truth" that he celebrated Christmas. The important thing to most Witnesses is that he "understood the Ransom." Anything else he did contrary to "truth," were things to be "corrected" by God later. This belief by the JWs renders completely useless any evidence, no matter how solid, that may one day be produced to indicate he had association with the Masons.
..and he disputed the Trinity, Hellfire and the Immortal Soul (the latter, in fact, which Masons used to have to believe in).
You've nailed it succinctly. JWs dismiss anything odd as unimportant, especially if it was in the far past. For this reason I suspect that no mother is genuinely going to throw in the towel over something so ridiculous. The "Generation" teaching is recent enough, maybe, but not secret society or even church affiliation.