Shouldn't, sure. But people use software in all kinds of sub-optimal ways, and it would behoove an author to make sure that it doesn't fail dramatically when this happens.
I'm not even sure it's suboptimal to shell out to grep instead of writing a bespoke search in Python. It would depend on the amount of data I'm sifting through.
You misunderstand entirely how much the author of any software with "achievements" cares about whether it works well in shell scripts and/or from python.
Grep is very optimized for what it does.