SpotMenus utilizes a feature called "App Clips" on Apple iPhones for loading menus. When you scanned the QR code at the restaurant using your iOS powered iPhone the "App Clip" saves on your device for 30 days, this is a feature/requirement of Apple/iOS and NOT something SpotMenus implemented or designed. If you do not use / open the App Clip for 30 days it will automatically delete from your iPhone.
You can also choose to delete the "Apple App Clip" from your device manually before the 30 days is up by following the 3 steps outlined by Apple at https://support.apple.com/en-us/HT211546.
If you downloaded the actual SpotMenus app from the Apple App Store you can choose to delete it by following the steps outlined by Apple here: https://support.apple.com/en-us/HT207618.