This is bizarre victim blaming. People tweeting their excitement about joining a company is totally normal and if anything should show they are someone who will also probably amplify the company’s social marketing.
I'm not trying to place blame, I would however like to warn readers of this board, younger ones who have grown up with social media and consider it normal to share everything they do, that a lot of companies don't think that "amplify [a] company’s social marketing" is an unequivocally good thing that they want their employees to engage in. When you're in a vulnerable position like just before starting a new job, why invite that extra scrutiny.