Look, I'm not going to defend the guy automatically, but for those who made blanket statements that "timing" must mean "cheating", I don't agree.
Even if I have a great poly relationship, if something dramatic has happened in my partner's life (death of a family member, lost job or whatever), that would be a horrible, selfish and irresponsible time to introduce the fact that you just met a potential person and that you want to explore a relationship with them.
But it really needs to be something concrete like that, and I wouldn't have any qualms about telling my potential about that. It would also mean, though, that the new relationship would be put on hold from developing any further as well. I don't get the sense that this is what is going on, here, though.
"Listen, or your tongue will make you deaf." - Native American Proverb