They could easily be testing many of the gmail + yahoo + other popular accounts as well, doing google searches in the background for "name@gmail.com AND company" to see if the person appears or maybe it really is more than what I thought.

I just thought this way originally because it showed "26 results" for a friend I looked up that I'm not connected to before it gave me the 1 final result that was his email. The 26 results as it was loading showed everything from first@company.com (not active), firstlast@company.com (not active), firstLetterlastName@company.com (not active), etc.

EDIT: So based on it showing so many false positives it looks like it's just queuing up all possibilities than returning whatever it finds works.