Yes, it's the same general idea as Windows. Or, I should say, the original Mac OS.
You probably already know all of this: In Mac OS 1 through 9, the system kept track of what files were, and what belonged to what by each item's Type and Creator codes. All EPS files had a Type of EPFS. To prevent EPS files from being locked to only one app, each also had a creator code. So, an Illustrator EPS would have a Creator of ART5, Photoshop 8***, and so on. Each the same file type, but they open in the app that created them when double clicked. Much of this carried on through OS X/macOS, which also uses file extensions to determine what is what.
Windows has always had the problem of one extension - one app. If you mark .eps files to open in Illustrator, there is no way to separate that extension out for the app that actually created it. So, if you double click a Quark XPress .eps, it will try to open in Illustrator. If you change .eps to open in Quark XPress, then all .eps files will attempt to open in Quark, including those created with Photoshop, Illustrator, etc.
That brings us to Snow Leopard, where Apple declared Type/Creator codes deprecated (dead). Now you're looking at the one extension - one app scenario. How do you keep .eps, or other files types that can be created by multiple apps from being locked to one app? Apple came up with Uniform Type Identifiers, which is written as part of each file data. Each app writes its identifying data as part of the file. When you double click a Photoshop .eps, the OS knows it belongs to Photoshop and not some other app.
Problem. You can break this method of app separation by clicking Change All. If I do that to an Illustrator .eps in Get Info and click Change All to open in Photoshop, all .eps files from there forward will try to open in PS, no matter what app created it. The only fix is to rebuild the Launch Services database so such manual changes are tossed and the OS once again pays attention to the Uniform Type Identifiers of each file so they open in their correct apps.
Anyway, your Mac is doing something it shouldn't. When you change Excel files to open in the Office 2016 version, that should be all you have to do. In no way should the OS be tossing the association back to Office 2011. At least, it's not supposed to. Since hydawaybottle was also seeing this issue, it may be a bug in High Sierra.
The only other thing I could suggest is to first do a full, restorable backup. Then, reinstall the OS. If even that doesn't help, than this is likely a repeatable bug.