Thanks for clarifying, that is not what the definitions I found via Google said

I can confirm that Google is wrong in this case. Sleeping outside without a tent is generally referred to as “dormir à la belle étoile”, but it is not necessarily implied in “bivouac”.

From my experience (which varies, the rules are local and not nation-wide laws) the difference is whether you can stand in your tent or not. I have seen whether you can carry your tent with your backpack used as a criterion as well.