“Keeping one day yom tov in Israel is neither a kula nor a chumra.”
He didn’t say it was either. You can’t decide how to posken based on what you think is “logical.” They asked their rov and they didn’t like his answer, so they did the wrong thing. No reason to complicate the story.
By the way, I also find the opinion (the Chacham Tzvi I think?) of going by where you happen to be more logical. The whole point of the thread is about going by your posek even when you don’t think the psak is logical.