It's something that has occured a few times, I specially remember 2018 Heritage Marcell Ozuna, because the Cardinals had just traded for him, his base card was in Cardinals uniform and his purple/chrome cards were in the Marlins uniform. That matches your finding this year with Downs, base is new team, chrome is still old team.
I would assume the chromes are made earlier in printing or their process doesn't allow for quick airbrush modification. There are a lot of airbrush cards this year in Heritage. I bought a Target Mega box and realized that both Murphy and Bellinger are shown on it in their A's and Cubs uniforms, same poses as the base, but the release card has updated team uniforms painted on.
The real kicker is on the Target Mega box there is a card for Nolen Arenado, which doesn't exist in the actual release set, so i wonder where that went???