If Tesla was actively working to prop up our fossil fuel based electricity grid, than I think this would be a fair argument. But they are not. Instead they are actively engaged in the solar+storage market, and they have stated multiple times that they believe the grid can be 100% renewable.

In the short term, yes, folks will need to rely on existing fossil fuel technologies to build factories, transport materials, and power the grid. That is because there is no other economically viable option. To expect the entire clean energy industry to bootstrap itself only using clean energy is a fallacy. In 20-30 years when the grid is more green and clean transportation is widely available, then arguments like these would be valid.