There are certainly Russian soldiers who knew enough about that war to make such an informed decision. But Putler is also using this war to perform an ethnic cleansing a genocide among Russian minorities from far east - recruiting people from communities with little knowledge about world politics and being very very poor. Buratya comes to mind. Low education + poor + pressure + promise of money and you will end up with a lot of recruits who had no idea what they were getting into until their own soldiers started pointing rifles at their backs from the second line should they dare retreat.