I’m guessing the person who offered this advice was in his/her 50s or greater. This was the accepted wisdom when I was in school back in the stone ages. Back then, few undergrad engineering programs were as rigorous and research oriented as they are today. Engineering PhD programs were also rather rare. As undergrads in the math program, we were told that the engineering PhD programs wanted people with higher levels of math than were required for a BSEE and that they valued the research skills that come from the physics programs.
Nowadays, undergrads in engineering programs are expected to excel at math and they are also given the opportunity to participate in significant research projects, so the rationale for preferring math and physics majors no longer applies.