I'm of the mindset Zelinskyy absolutely knew, but purposefully kept denying it was close on the horizon to calm his people and also not be accused of saber rattling. It was a de-escalation and obfuscation tactic in my opinion and I think it sort of worked to the ends he intended in subtle ways. Ain't no way you see that many troops massed at your border and think "Putin? That guy's chill. He just doing some exercises. He wouldn't be planning to invade me on the heels of an Olympic closing... Again."