The timestamps on your XMP files are simply recording when they were created, which is whenever you loaded the pics into Lightroom, or Bridge, or whatever. They're totally irrelevant.
As a matter of fact, the date/times on your CR3 files are also totally irrelevant. That timestamp records when that physical file was created. So for example, if you copied a pic from a memory card to your computer, it could be the date/time that the computer copy was created. Or, it could be copied from the original file. It could be either way, depending on exactly what software you use to do the copy.
I have tons of old media files on my computer whose timestamps are complete garbage. It's the time the file was most recently copied, or restored from backup, or transferred form my previous computer, or whatever. Bottom line, the operating system's meta-data for your files is for the operating system's benefit, not yours.
What you should be looking at is the meta-data inside the image file itself. Because this data is inside the file, it gets copied intact along with the rest of the image; so this tells you about the content of the file -- i.e. the image -- as opposed to the physical manifestation of the file on a particular disk drive.
For example, in Bridge, you could look for "Date Created" under IPTC Core, or "Date Time Original" under Exif. Those will tell you when the picture was actually taken. Don't look under "File Properties", that's just the file timestamp again.
