Hmmmm -- surface level, that sounds like light usage, but it also might depend on how many images were loaded and what the file sizes were, or if there were graphics on any of the sites you visited?
What type of mobile hotspot are you using?
Marissa brought up some really good points about where the data consumption could be coming from. Can you tell us what hotspot device you're using and if this is still going on?
(I tried to respond a few days ago, but my data was so throttled that the site wouldn't let me post my response.)
I have done a number of Google Image searches during the time of the alleged data consumption, but probably not more than 10-15 a day (at a generous estimate).
As for what kind of hotspot, the range is set to "Standard" (which is the lower of the two possible options). Besides this, the only "Settings" options I see for the hotspot network have to do with encryption, and the list of allowed devices.
The device I'm using is a Galaxy Avant that I purchased three years ago, running 4.4.2 of the Android OS.