++ EDITED REPLY, rephrase an explanation 4th paragraph (from top to bottom).
How are you able to browse cloud documents from Acrobat without using File => Open?
Seems like you are referring to the section "Other file storage".
If this is the case don't use that method.
Having the settings configured as I've suggested works for me with OneDrive when using Open => File => OneDrive online folder from the Adobe Acrobat program ( not by going to the Home workspace and clicking directly over on the left side "Other file storage" as you've pointed out).
It only displays pdf files regardless of MS Word documents or other file types already saved in those same folders.
However, if you are saving to the OneDrive cloud folders via "Save As" from the Adobe Acrobat program it will show all file types as you navigate through them.
As I was reading in some Microsoft support forums, this could be a design behavior of how the Sharepoint/OneDrive clients interface with other hosts programs (like Acrobat), it doesn't seem to be exclusive of Adobe Acrobat.
It happens with web browser too and there is no current workaround to modify what file types to view only.
Yes, "Other file storage," which is a list of all the sites you've added. You see the same thing in File/Open, which is why I was surprised that File/Open does filter out the other files, bit it must be written to do so Otherwise, the two areas look all but identical. That's OK, I'll try to encourage people to use File/Open.