Apparently, what's happening here is that Google Play support libraries get auto-updated regardless of your update settings. If an app you installed relies on those libraries, an "update" to the app is triggered, even if no code in the app has changed, only some libraries it uses.
Since there isn't a way to stop Google Play auto-updating, there isn't a way to stop these app updates either.
Google made a change recently to the Play Store and the visibility of certain updates that used to occur silently. Now, when Play Support Libraries are updated, it will cause apps to "update" if the update replaces the support library version an app is relying on, so the app is essentially reinstalled when this happens—but with the only change being the Google Play Support Library version—not the app's code. The support libraries are what brings newer Android API features to older Android versions without having to be on the newer OS version (it doesn't bring everything, but it improves compatibility, allows for a unified experience across Android versions, and does sometimes bring features). So the older the version of Android, the more this is going to happen, since the older the OS version, the more the support libraries have to bring to that older OS version to bring it up to date.
And since Play Support Library updates can't be disabled, neither can the pseudo-update of the affected apps. There's no new code from the developer. It's just Google updating their part, and the app being rebuilt around the new update.
Source + more info: this Reddit post
