Dan Telvock, a local reporter in Buffalo who covers the solar gigafactory which taxpayers bought for Tesla, is already calling out Musk on his "aspirational" BS. https://mobile.twitter.com/DanTelvock/status/115621452719479...
Regardless of which one is correct, the fact remains that they are scaling up a new technology. Both 200 and 1000 are ambitious goals, and both contradict your implication that the solar department is "a shell of its former self". It has dramatically shifted directions (from market standard solar panels on roof, to integrated solar roof tiles).
Of course normal companies, with a level of corporate governance ranking somewhere above "drunken frat house," publish these sorts of production forecasts in official channels after careful vetting and consideration. It is neither admirable nor acceptable for a public company CEO like Musk to simply pop off on Twitter with "ambitious goals" on which investors might rely for trading decisions if they have no basis in fact. Which is why questions are already being asked about whether Musk's tweet violated the terms of his amended SEC settlement agreement, which requires legal pre-approval for any public statements he makes about matters relevant to Tesla, including production forecasts. https://www.bloomberg.com/news/articles/2019-07-30/musk-twee...
Most of Musk's company goals are aspirational, and the means to the end often change. For example, Falcon 9 first stage was supposed to be reusable by landing it in the ocean with a parachute, but they found it didn't work. Instead, they lengthened the first stage booster dramatically so it would have the propellant margin to land propulsively.
[1] https://twitter.com/elonmusk/status/1156005185656782848?s=20