For this to happen, you would have the IB checkbox enabled for “guests must not have a negative review” AND the applicable Guest received a NO by some prior host for “Would you host again”. Regardless of Stars!
The stars are actually meaningless. Air is intentionally very tricky about what that feature actually means - rather than what it should mean.
So - some host in their past did not want the Guest to KNOW they actually sucked - but wanted to prevent them from some IB opportunities.