I can understand the trackable owner doing this. They may be concerned about it being stolen, or they're "sending it out again" after it had been stolen. But someone else making a list of your trackable's number and sharing it with someone else when you don't have it or the picture copy with you is definitely not in the spirit of the activity. Neither is just trying out numbers on the website until you find ones that work, which must be the case for the person who logged mine and The Lost Patrol's trackables. It was the same person for each of us and no one else has entered a log of "discovery" for them.
Their stats currently show 18547 trackables, but it was a bit higher until I hit refresh. It will drop by another 5 once I delete their logs of mine.