The Play Store maintains your list of purchases. The dev would have had to build a new APK just for you with ads disabled.

False. APK binaries, no matter paid or free, are built and deployed in a standard manner across devices. Google Play backend either has app bundles or APKs that are standard across Android, and the only differentiators are either DPI targets or ARM7/ARM8-64/i386 (last one is Intel Atom et al) ISA targets.