IIRC, Tesla's ESPP plan is priced during the first week of February and August, and the employees get a 15% discount to the lower share price at the beginning and end of each semi-annual period. (Check out TSLA's share price in early February, 2016.) IMO, ISPPs are a bird's nest on the ground benefit, and smart employees cash out as soon as they can to re-load over the following six months.
I'm not saying ESPP sales were a material factor in the share count increase you noted, but having tried to reconcile share counts increases to Form 4s over multiple quarters I have formed the impression the ISPP is not inconsequential in the share count accretion.