To that end, observing unanimous behavior may imply some bias.
Here, it could be people fearing being a part of the minority. The minority are trivially identifiable, since the majority signed their names on a document.
I agree in your stance that a majority of the workforce disagreed with the way things were handled, but that proportion is likely a subset of the proportion who signed their names on the document, for the reasons stated above.
So clearly this wasn't a 50/50 coin flip.
The question at hand is whether the skew against the board was sincere or insincere.
Personally, I assume that people are acting in good faith, unless I have evidence to the contrary.
But future signees are influenced by previous signees.
Acting in good faith is different from bias.