I don’t see why this is not an act of treason. Is a soldier in the field the right one to decide what is a “lawful order”? Are they mature enough to refuse orders? Nope. Throw these people in jail and try them for treason.
I think what these people did is slimy and wrong, but that's not because soldiers should be presumed unable to distinguish between lawful and unlawful orders. Nor does it qualify as "treason".
People throw around that word far too often while apparently having no.idea of what it means legally.