It's not quite even that - he wanted to bail out his cousin's failing solar business with Tesla shareholders' money, but to try and justify it, they pretended that Solar Roof was a fully developed, ready to sell product that was going to be revolutionary and worth buying SolarCity for, when it was actually just a concept they'd quickly come up with and some 3D renders.

They actually had to develop it (with Tesla shareholders' money) after buying out the failing SolarCity.