First, Wong was not traded. Wong is a free agent. The Cardinals let him be one.
Second, interesting question. Let's first discuss the vesting option. It hinges on him getting 550 plate appearances, at a minimum, in 2021. If there are less than 162 games next season, then precedent says that will be prorated. That's how it works for this past season. In addition to the 550 next year, he must get 1,100 total in the two seasons to vest the option. He had 169 plate appearances this season. Prorated for a 60-game schedule -- even though the Cardinals did not play one -- that's 456 plate appearances. That means he needs 644 plate appearances to reach 1,100 for the two seasons. Only four times in his 10 years with the Cardinals has he had that many.
It gets interesting if his side argues that he had only 58 games to play.
That jumps the prorated plate appearances to 472, and means that he only needs 628 to trigger the option. As an everyday player, he has reached that number -- oh, hey, only four times in 10 years. So not as interesting as maybe it would seem ...