cursor selecting, moving, grabbing as passes over all pages

I don't know if this erratic behavior is how the cursor is supposed to work in Sierra or if I have a problem. I have a month old MacBook Pro. Several days ago, the cursor started started selecting everything it passes over. Sometimes it grabs a page, such as in Mail or Safari, and everywhere I move the cursor the pages moves. Trying to stop it is like trying to shake bubble gum from a stick. worst, if I pass cursor over Dock, cursor grabs an app and moves it somewhere else on Dock or even from Dock.

Did I set something accidentally? I checked several things in Support. In Pref > Accessiblity > Mouse & trackpad > Trackpad options, I have enabled dragging with drag lock set. But obviously dragging is happening without drag lock, at least as I understand drag lock. Read a post where someone suggested 3-finger dragging. Would that help?