Why are some icons on files on my TimeMachine drives changing to Word?

I was looking for instances of a particular file on my TimeMachine drives. These are .mov files. On most of them, the icons are correct, showing a frame from the movie. But on the others, the icon has changed to a Word icon and can't be opened. What's going on?

I just noticed that these files are aliases! Why? And they appear not to reside in any folder!

See screenshots below. The ones with the Word icon have changed overnight when bringing up the same search again! TIA!

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