On the other hand, if you are constantly working with certain systems, you will know this stuff. If they ask me something esoteric about a language or API that I know really well, I can answer all the tricky questions, or explain how I think it would work. If it is something I use rarely, then I could not.
I think these kinds of specific questions are justified, but only on the basis that (a) it tests that the candidate really does or has worked in this field in depth, and (b) you have a bunch of other similar questions, and knowing the answer to just one or two of them counts as a pass. Basically, it's like throwing spears into an opaque pool, hoping to find evidence of the salmon of knowledge.
I could totally see asking someone that question if they said that they were intimately familiar with some distro or another. Outside of that context, it seems like a really bad question. Maybe there was another purpose to the question (like seeing how you reacted to bad questions), or you just had a shitty interviewer.
Just checked the mkfs.ext4 man page and no, that doesn't seem to be the case. This was about five years ago so the precise question I can't perfectly remember, but the nature of it was as stated; It was a question about a specific filesystem setting default value, on a specific version of a specific distribution of linux, inode size, bytes per inode or bytes per block.
Apologies for sounding a little addled but it's been five years since I have been a systems administrator so it's all melted together in my memory.
-b block-size
Specify the size of blocks in bytes. Valid block-size values are 1024, 2048 and 4096 bytes per block. If omitted, block-size is heuristically determined by the filesystem size and the expected usage of the filesystem (see the -T option).
I remember that Red Hat and Fedora used 1024 on my computer.
As for the distribution specific thing, maybe some distribution had their own version of /etc/mke2fs.conf (settings for mkfs, including block size).
Anyway, isn't block size standard across all OS?