To me that's not "different decor" - the theme is "your travels".

Yep... you have a theme there!

Well, it's travels but still may not be that obvious, unless you hang a map with push pins and additional travel artifacts.

i don't know what the rules say, but i don't think a room needs a theme!

Maybe it depends upon whether or not all of the colors work together? Or, mat/frame them with specific colors that will also pull your travel theme together?

Thanks everyone! Clearly I'm overthinking this.

I think a lot of bathrooms seem to have a theme because they are too small for more than one or two pictures, so it just seems like a theme. The pictures in my master bath have a theme I suppose just because I was too cheap to buy any pictures when I was doing it and just picked out some photos I had. If I got to buy something, I'm sure the pictures would relate only in that I liked them.