I agree, wbenson. There is every reason to believe that HMQ couldn't care less about such allegedly, infra-dig comments. Indeed, there's considerable evidence to the contrary.
That she'd encourage her grandson, William, to cut his relationship with anyone, based on what his friend's mother might or might not have said, is high fancy ,and something of an assault on Her Majesty's frequently and keenly observed ,common sense.
Critics are confusing Queen Elizabeth's imagined opinion with that of Nancy Mitford's "U and Non-U" which is, today, regarded as an outdated fossil of aristocratic life, though it does have a certain archeological charm.