The Smart Collection you posted seems to work here, at least when I tried it. That being said, I have ran into problems with different Smart Collections involving DATES (different date tests) for several versions. It seems to be random and not repeatable. I will have a known wrong count for the Smart Collection and then do an Edit Smart Collection and Save and the number will update. The Library filtering/smart collection seems like it has been buggy for a long time and could use some TLC
is there a place in the Metadata panel that shows the edit date?
No. And you can't even make a custom tagset for Metadata panel that shows it (I just double-checked).
However, the Search Replace Transfer plugin will expose it, and you can then filter on its value.
Can anyone provide a possible explanation?
Edit Time gets changed when you change a metadata field. Any chance you changed caption, color label, or some other field? Any plugins installed that do background scanning?
Also, did you use the Any Filter plugin or another plugin that uses custom metadata fields under the cover? E.g. Any Filter flags each matching photo by writing into a custom metadata field, and that causes LR to think the photo has been "edited", bumping Edit Time.
I'm quite sure that the only thing I did when I got home was actually edit 3 photos. I was not changing metadata fields that I know of, normally when I am in editing mode, I don't go back and forth from editing to metadata to editing to metadata. The AnyFilter plugin is not installed. I doubt that the other plugins were doing anything, the only one that would possibly be active is Jeffrey Friedl's Lightroom Exporter plugin, and it is my understanding that it doesn't download comments from Flickr unless you cause it to run by using it to upload photos.
This morning when I woke up, I tried creating the smart collection anew, I am 100% sure that I have not edited any photos since midnight or changed the metadata in any way, since I was asleep and Lightroom was closed (I'm also sure I don't sleep walk, and that no space aliens came into my house and used Lightroom without me noticing). I launched LIghtroom and created the same smart collection, which should produce zero photos whose edit date is "Today" (June 8, 2016). Same 91 photos were in the smart collection. I will report this as a bug, but if anyone has any ideas, please let us know.