It's not really a weird question, but perhaps an illegal one. Seeing as how we have a law of conscription, it's theoretically okay for an employer to ask if you've served, but they can't deny your employment simply because you either didn't serve or chose civilian service.
Also, since they can ask if you've served, they can pretty much just slide the whole military/civilian question into their original question. "Have you served in the military?", my boss asked me during my interview. Legally, he was just checking if I still had a term of service ahead of me, as they're legally supposed to hold my job position for me for the duration of my service, and might opt for a short term contract instead. I knew, however, that he was also getting to know me. It's not fair, that my service record affects my chances, for better or worse, but it's a fact that most employers prefer a military background, rather than a civilian or prison one.
Luckily, mentioning that I had served a full year triggered a casual follow up question, "an NCO, eh?", which immediately earned me points, fair or not.
So yeah, not really a weird question, just a really sneaky one.