More than one possible reason for the talks
Apple have IIRC patents on lithium battery technology that they use to get cells shaped precisely to fit the available space. Tesla could be interested in that.
Dashboard integration of entertainment functions is another possibility.
Tesla are working on cheaper offering than the Model S, which uses a (presumably very expensive) 17 inch touch screen. They could be trying the idea of replacing that with an iPad in the upcoming model.
I can't honestly see Apple wanting to go into car building though, or thinking about buying Tesla, it doesn't match up with their approach to entering new markets and car making is too far from their existing markets.