I assume he is implying that the technical incompetence caused people to second-guess what they heard when confusion arose. This confusion can be misunderstood by the interviewer as confusion over the subject matter. I know I've had that problem before over poor telephone connections.
People who have any kind of trouble communicating verbally with normal native speakers of the language in which business is to be transacted, are not a great choice for jobs which require clear communication.
People who are poor communicators should generally not be in leadership positions. It actually wasn't just the accent, as his written English was absolutely awful, too.
He also had a really thick accent. Later, he also proved to be technically incompetent.
I quit after 6 months.