Theme Generating Unecessary Pages/ Duplicate Content?

I recently noticed that Google is indexing a bunch of pages from my site that it shouldn’t be. Some, like the image attachment pages make sense to me (and I understand how to noindex them in Yoast).

Others, I don’t understand why they’re being generated. I spoke to my hosting support, and they said since it’s not a default WordPress thing, they may be created by theme settings.

For example, there’s multiple posts that were created with all the content on a single page (so there shouldn’t be a page 2 or 3), but these posts now have variations showing up in Google’s index with a 2 or 3 appended to the URL like this:

https://choosytraveler.com/best-travel-books-2017/2/

I also don’t understand what this is, it looks like an attachment page, but it has multiple images on it (and again, my hosting support says this format isn’t WordPress default):

https://choosytraveler.com/fuji-xt2-best-travel-cameras-2017-125/

The attachment pages with multiple images are just sort of weird to me, but mostly I’m concerned with preventing the theme from generating duplicate content with slightly different URLs. What is going on with the first example? Can I stop it from happening?

So WordPress is actually generating these extra pages with numbers at the end of the URL? I guess it makes sense to me what you’re saying about being able to add any numbers to the end of the URL, I’m just not clear on how Google ends up indexing URLs that should only exist hypothetically.