Consider the following code:

<div role="button">Button</div>

This passes aria-allowed-role. But if you configure the rule to not allow implicit roles, it now fails

axe.configure({
  checks: [
    {
      id: 'aria-allowed-role',
      options: {
        allowImplicit: false
      }
    }
  ]
});

The reason is that the final if statement in the check will always pass unless the element is a tr node inside a grid.