Bounce emails going to Unverified outside email id

We have a verified identity to sent emails using SES and we do receive the bounce emails to the verified identity as it was used as sender email. But for one of the broadcast, some of the bounced emails went to a collogues Hotmail email id which is not a verified identity. We received and email from AWS that unacceptable levels of negative feedback about email sent from your account has been received from a provider. What would be the reason of the bounce emails sending to another email?