You're not crazy and you're not alone. I have the exact same problem on my laptop, but not on my iMac.

The Macbook Air shows version 10.0.1 in the Applications Folder, yet the App Store shows no updates available and that version 10.0.2 was already installed. I know I went through the installation process for iMovie, but somehow it is not showing as installed, or very possibly, the version number is wacky.

When I did the iMovie update on the iMac, it seems to have worked, in that it shows 10.0.2.

Go figure! Why any of these blips of electrical charge actually work the way they should is still pretty amazing to me. smirk
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On a Mac since 1984.
Currently: 27" iMacs, Macbook Air, macOS 10.15.x,; iPhones, iPods and iPads galore!