You’re approaching it a bit too narrowly. When I talk about implementing other activities as extensions of the combat mechanics, I don’t mean those activities literally involve shooting things with guns, though that’s not necessarily off the table, either – there are games that are so intensely combat-focused that you can only interact with the environment by shooting it!
Rather, I’m talking about the types of interactivity that are prioritised by the game’s physics, user interfaces, and so forth. The Bethesda Fallout games are basically designed with tactical movement in close-quarter skirmishes as their top priority, and all other ways of moving about or engaging with the environment are treated as extensions of that – which can make some types of exploration very awkward.
This design pattern can be kind of invisible because a lot of games do it, so it can be useful to consider counterexamples; you might look at, say, any number of Legend of Zelda titles for examples of games where the ways that you move and interact with environments prioritise puzzle-solving rather than combat – often to the extent that combat mechanics are treated as extensions of puzzle-solving mechanics, rather than vice versa.
Another good example might be Shadow of the Colossus, where the combat system is literally an adaptation of the rock-climbing system; this one goes far enough that combat is rendered awkward for the sake of consistency with the exploration rules in much the same way that many other games render exploration awkward for the sake of consistency with the combat rules.
(Granted, the Bethesda Fallouts are something of an improvement in this respect; the Interplay Fallouts have such an intensely combat-centric UI that you’re obliged to plot your path on a combat hex-grid even when you’re just walking around town – which is kind of hilarious, given that they offer non-violent resolutions to nearly every confrontation.)
