> And, the photo looks like it has single pane windows with snow outside? They might not have had functional multi pane windows when the home was built?

That's water outside. After a storm. That's a waterproof house in a coastal area of Germany that tends to flood during storms.

Needless to say those windows are designed with another problem than just insulation in mind. I can't tell you whether they're multi pane. All I know is that they open towards the outside rather than the inside for obvious reasons.