Thanks, hadn't seen that, and the same OS version wasn't in the old style System control panel. (Windows is such a mess these days...)
I'm on Version 1703, Build 15063.413 in that case, and was not seeing the extra menu item.
But after associating the Photos app with a file type, I am seeing it now. (I'm sure I tried this earlier but didn't see it, so it may only happen with a combination of the Photos app being default, and a recent OS update.)
Setting something else as the default for the file type also gets rid of the menu item again, which is rather strange and non-standard. But also a quick way to fix things, unless you really want to use the stock Photos app.
Now that we've seen it on our own machines, we should be able to add some kind of fix or workaround for it.
Many thanks to everyone for providing info in this thread.