Exactly.

No one was stopping them from saying what they said. However, when the agreed to work for the company, they agreed to abide by the companies rules. And if they were suspended, they obviously broke one of those rules.

They were of course free to quit at any time and say whatever they felt like saying, at which point they would not have been subject to any penalties whatsoever.

Never for a second were these three subject to limitations on their right to free speech. These three however were subject to the terms of their employment, terms which they clearly broke.