Where did these caseback scratches come from?

[Qristian]

Hello,

Couple a months ago I bought myself a preowned 1,5 year old V-series Milgauss (not from original owner). The watch itself is perfect, but only thing that bothers me a bit is that there are small hairline scratches in a watches caseback and I don´t have any idea where did they come from...

As you hopefully see from these poor pictures of mine, the scratch pattern is a bit shaped like a "sandglass". So I wondered, if you might have any idea what might have caused these kind of scratches? I have couple of ideas: A) Watch winder, B) Nato strap + sand between, or C) killer armhair. Well, I know they can be buffed away, but the origin of these kind of scratches still interests me...