I think Mitch claiming no binding vow is too risky for scum. It's implied that almost every role has it. Or at the very least, nothing about binding vows not being a universal mechanics. So claiming they don't have it is drawing unnecessary attention to themselves.
I don't think any scum would alter the fake claims provided to them. So, if it is a fake claim, it would have to be made by Ekko himself. Would he give a painted target as a fake role to someone?