The user experience on Android is never standing still, which is no more evident than in the Play Store itself. It seems Google may be trying out a new behavior for search queries that match the names of the Play Store's predefined categories. Instead of presenting a list of apps, searching for a term like 'action' or 'puzzle' can bring up structured lists like those that would appear in the category itself.
A search from the top level of the Play Store still pulls results from each of the major stores, as it should; but tapping into the apps section from those results or starting the search from anywhere in the Android-related portions of the store can redirect to the category-oriented view. It's likely that Google is adding this as a shortcut to help inexperienced users find categories if they've never browsed through the Play Store before.
It seems that this change in behavior is only showing up on specific accounts, so it's either just starting to roll out, or it may be a limited public test. Based on what we've seen, some category names still don't show the matching sub-lists, which may suggest that this functionality isn't quite finished. It's not clear if these are the only changes to search, or if there are other special terms, so keep an eye out for anything out of the ordinary.