Hi Shai,
The endpoint returns the top 50 results, so it is not an exhaustive list of all venues with that category.
That said, we're also sorting out some lingering issues regarding the indexing of venue categories in our new search system, so it's possible that you'll see periodic cases where category filters don't completely work as fully expected
~ak
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Akshay Patil / Foursquare Platform Evangelist
@akdotcom / @foursquareapi