A normal interaction does not involve talking about your visa being revoked. As others have pointed out just applying for asylum in Canada often leads to US visas being cancelled. Is he also using his old passport? He should really be verifying whether he has a valid US visa. Would also suggest getting a new visa because you can’t use your old passport and would not want to be travelling with my home country passport. The person situations has changed dramatically so it would be perfectly understandable for US to cancel their visa. PR does not guarantee a US visa. Having a job, savings, a good reason for travel, your status in Canada, etc. are some of the things considered when applying for a US visa.