Maybe not the biggest factor, but still definitely a factor.
The link between gas prices and electric vehicle sales is a tricky one to nail down. It's hard to imagine that anyone paying the kinds of prices that Tesla is charging would then decide not buy a Model S just because gas is a couple of bucks cheaper. But there are more mainstream EVs, and the fact of the matter is that when gas prices fell 40% over the last year, hybrid and EV sales also dropped, albeit by a less dramatic 3.7%.
BMW, the makers of the mainstream EV i3, are concerned by this. As Ian Robertson, BMW's head of sales and marketing told Bloomberg “Sales of the zero-emission vehicles will probably dip in some countries, including the U.S.” And there has indeed already been a dip, but BMW, unlike several other carmakers, has decided not to let this alter its electric car strategy. Although gas is cheap now, and will quite possibly continue to get cheaper, emissions regulations in the US, Japan and Europe will continue to get tighter, and BMW sees EVs as the ideal way to deal with the issue.