It's a Japanese convenience store, so seeing a foreigner is weird for people on it's own.

Add to it that the foreigner is something like two meters tall, and towers over absolutely everyone that the average Japanese person has ever seen.

It would be like a Westerner seeing someone walking around the corner store in full samurai garb, in terms of "they'll never believe me unless I get a picture"-ness.

So it's quite possible that whoever took the picture didn't mean anything by it.

…

That said, it's still a late night corner store, so yeah, it could be someone was creeping.

That's a perfectly valid explanation and something I didn't consider. I'm glad I can express my views like this and be challenged in ways I never would have on my own.