Data caps are a real thing now and the concept of unlimited data is a thing of the past. While manufacturers have realised this and implemented settings that restrict downloads/streaming to WIFI, there still exists room for improvement.
Fortunately for Android users (at least ones on the newer versions) Google has added a setting where you can tell the device that the ‘WIFI’ connection you’re on is actually a portable hotspot, so it shouldn’t go crazy downloading Play Store updates or anything else that will consume copious amounts of data.