Don't people talk differently depending on the company they are in? I think most people will have different levels of trust in their acquaintances, at the extreme what I might say to my significant other will be different to what I talk about with a work colleague.
The problem with social media is that it is typically a megaphone to everyone.
Absolutely, and it is completely normal. The Japanese even have this concept explicitly ingrained in their language - 'Tatemae' (socially acceptable reality) and 'Honne' (informal, personal reality) [1]. This is essentially the difference between saying "I'm fine" or "Actually, my dog just died" to a random person or to your close friend.
But is it really so much that you're broadcasting, or are others eavesdropping. While it would be weird to say that to a stranger, in facebook your ostensibly informing your friends. That might make difference.
If you can say something with one group of friends, but need to change or hide that to speak to another group, are you being authentic?