Cursor hover behavior

I am using a 2017 MacBook Pro 15", 2.9 GHz Intel Core i7, 16 GB 2133 MHz LPDDR3, running High Sierra 10.13.3.

I use the trackpad for navigation. Whenever I hover over something for more than a second or two, it interprets that as a mouse click, and opens the file or executes whatever action is appropriate for where the cursor is. I've tried looking at the trackpad and accessibility controls in Settings, but haven't found anything obvious that would be causing this, or how to turn it off.

Help!