Rubbish, Ukraine was threat in that sense because it wanted to become more aligned with a Western Democracy, it's membership of NATO is utterly irrelevant. If anything, Ukraine's desire to join the EU was far more of a "threat."
NATO has always been an excuse for Russia, they don't feel militarily threatened by NATO because NATO has never made moves to invade Russia (because Nukes). NATO responds to Russia's threat not vice versa. Russia understands this perfectly well
EDIT: Leading up to this Ukraine was at least a decade away from joining NATO and as long as it had border disputes like you know, with Russia being on its territory, it could never join. The only way it could have joined would have been to voluntarily ceded its lands to Russia and it was never going to do that. Russia fully understood that, which is a huge reason why it invaded in 2014 and annexed Crimea etc.
NATO is and always has been an excuse.