Even if you start from the premise that it makes sense for Tesla to be in the solar business, it's hard to rationalize that the best way to break into that market was to buy a debt laden solar panel installer.
I don't buy the short's narrative that this is anything like an Enron style fraud but the only point that the Tesla short sellers are a little bit right on, among the mounds of BS they publish, is that the Solar City acquisition was a shitty deal and Tesla would be better of today had it not happened. That said I don't think it is going to sink the company the Model 3 is just too good.