When pairing an Apple Watch to my iPhone, I've noticed that even though the App Store lists all of my apps being up-to-date, the Watch app on my iPhone states that several of my iOS apps will be updated for compatibility before their watchOS counterparts will be sent over to my Watch. Is this a standard message that appears - even if all iOS apps on the paired iPhone are fully updated to the latest versions?
WatchOS apps are a complex hybrid since they started as all being dependent upon iOS and now they can be independent or dependent. You need to get both sides synced in some cases, hence the message to update iOS when watchOS is in play with one or more paired watches.
To be clear - some updates only apply if the watch component is required to be active or the developer ties them together when submitting their builds to Apple. This is all standard and you might even learn that some apps get different builds based on different hardware - not all apps are monolithic based on hardware versioning and software versioning. (Like an older watch that’s still supported but not the latest watchOS might get a different app than the latest watchOS gets).