A quirky out-of-the-box thought
Since he challenged the other team's offensive play catch
This is when the other SF team was rolling pretty well in the first half . In basketball timeouts can be used when the other team is rolling and you need to disrupt their rhythm and give your guys a chance to regroup
First thought: curious on the average length of a challenge vs a timeout. A timeout is 2 minutes. If a challenge on average is longer, perhaps you could call a challenge to disrupt the game even more than a regular timeout. If the average NFL challenge is longer maybe he did it to give his guys on D more time to regroup
Second thought: if the other offense is rolling, and you just call timeout, it could be seen by the other offense is smelling blood. But if you put into doubt a recent play with a challenge, it might put them on edge and be more disruptive
Just some creative thinking ...
But yeah, I'm guessing it was just an unnecessary challenge.