The notion that "what you do on company time belongs to the company" is one possible relationship between labor and capital, but far from the only one. And even that phrasing is a little misleading, because executives often get much more latitude here; the principle in practice seems to be less about serving the collective interest of all stakeholders (that is, the company) as serving the power structure's current occupants.

Many companies are pretty flexible about what you talk about as long as giving out the information doesn't cause immediate harm. It's not unreasonable for people at much stricter companies to complain that their company is being unnecessarily strict in ways that are detrimental to the employees.