It might not be an official station, since it's purpose was to test the battery swapping, so the cost of connecting to the main grid might have been too expensive.
Read this related article, one of the most interesting I've read about Tesla I've seen. It talks specifically about this swap facility. Basically this one charging centre allows Tesla to claim hundreds of millions of dollars of electric vehicle government-funded rebates due to a condition of the rebates. If this centre is in fact powered by diesel, that's a whole new level of irony.
It mentions how Tesla is able to maximise it's electric car rebates by making at least one centre that can offer a fast swap capability, even though practically all (or all but one) of their customers do not and can not charge cars this way. Having a fast recharge was a key requirement to qualify for the rebates.
I think a lot of people are being misled by someone with ulterior motives.
There are other charging stalls at that Tesla station. It has demand higher than expected and as a result they needed to put a temporary generator to reduce wait times.
They might be using this as a test opportunity for seeing how feasible a generator is for charging a Tesla.
The "government funded" part is referring to state legislation, not federal.
The swap system is not open to all Tesla customers, it's invitation only to a few because they are still working out the details. Hopefully California put in it's grant program requirements that it will only give rebates for cars that are eligible, if not, then can you blame Tesla for taking the grant money? Is there even any proof that they are taking grant money or is everyone pulling the "hundreds of millions of dollars in rebates" out of thin-air?
Last, newer diesel generators and ultra-low-sulfur diesel fuel make this method of power very attractive. It might even be better than coal-powered plants that transfer over the grid due to losses and conversions.
http://www.doosanportablepower.com/en/products/generators
It might not be an official station, since it's purpose was to test the battery swapping, so the cost of connecting to the main grid might have been too expensive.