Answer:
it's true
The requirement that all Supreme Court justices must have a background in law is derived from the U.S. Constitution itself. Article III, Section 1 of the Constitution states that "The judicial Power of the United States, shall be vested in one supreme Court, and in such inferior Courts as the Congress may from time to time ordain and establish. The Judges, both of the supreme and inferior Courts, shall hold their Offices during good Behaviour, and shall, at stated Times, receive for their Services a Compensation which shall not be diminished during their Continuance in Office." This clause sets up the basic structure of the federal court system, and it is generally understood that the judges who sit on these courts must have a background in law in order to be able to properly interpret and apply the law. Additionally, the qualifications for Supreme Court justices are further detailed in Article II, Section 2, which states that the President "shall nominate, and by and with the Advice and Consent of the Senate, shall appoint Judges of the Supreme Court, and all other Officers of the United States, whose Appointments are not herein otherwise provided for, and which shall be established by Law."