That's just what former Chief Justice Rhenquist told an interviewer,except he also followed up with, "whatever that means."
“Learned in the law” could possibly mean they read “Writing a Will for Dummies.”! But I think hy wrote it that way so that solicitors general (like lawyers in general) do not always need to go to law schools to be admitted to the bar. Virginia and California allow people to become lawyers by simply “reading the law” as part of an apprenticeship (this is how Abraham Lincoln became a lawyer). There have been a handful of USSC justices who became lawyers through the the “reading” method.