This sounds like it might be the "culture fit" rationale that interviewers have in mind when doing things that are really unfair to individuals (and, IIUC, in many cases illegal in the US).

Besides being unfair, it can also be otherwise bad for the organization. In tech startups, we talk about innovation and ideas, and one of the places that comes from is combining knowledge from different backgrounds (in multiple senses). If a startup started with two people who then only hired people like themselves, they're restricting the likelihood of good ideas that they wouldn't have thought of themselves.

I’ve had coworkers with Muslim-sounding names before and casual work conversation was about the same. It’s not like we usually sit around discussing religious doctrine.

That sounds an awful lot like racism to me

Completely agree, they really could be anything. What if they are a jelly-fish like creature that only communicates through touch?.

I wouldn't even know where to begin having a conversation with such a thing.

Which is a bit ignorant, don't you think?

This concern should have been addressed, if it really materially affects performance on the team, and this is a big IF, in the dreaded cultural fit part of the interview and not like that where they openly discriminate against him because of his religious background.

or, maybe, as seem by now: the post is entirely false

an approach, but most things we consider racism from the 1960s and before had an economic rationale or a social rationale, many of the people who normalized it at the time also didn't feel actual disdain in their hearts and yet we now call many of those things racist and have modified

so its just not an excuse

to assume you have nothing in common because someone has a foreign-sounding name is racism