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.
Goto Settings > Data usage > Options (the three dots on the top right) > Mobile hotspots. There you can check any WIFI connection and the phone will then be circumspect when pulling data through that connection.
I regularly tether from the LTE connection on my iPhone 5S and it is a relief knowing that my Nexus 5 suddenly won’t start downloading a 1 GB update to Asphalt 8 thinking its in a WIFI zone and thus saving me cellular data.