So you don't think that a 30-06 or a 308 would do the same?
There were plenty of examples of guys getting holes through their helmets from WW I onward.
She might be technically correct, however, because punching a hole in a helmet was part of the design specs, something that started happening around that era as the military/industrial complex really started moving along at ludicrous speed.
"As a result, the Army was forced to reconsider a 1957 request by General Willard G. Wyman, commander of the U.S. Continental Army Command (CONARC), to develop a .223 caliber (5.56 mm) select-fire rifle weighing 6 lb (2.7 kg) when loaded with a 20-round magazine. The 5.56mm round had to penetrate a standard U.S. M1 helmet at 500 yards (460 meters) and retain a velocity in excess of the speed of sound, while matching or exceeding the wounding ability of the .30 Carbine cartridge. This request ultimately resulted in the development of a scaled-down version of the ArmaLite AR-10, called the ArmaLite AR-15 rifle."
From https://en.wikipedia.org/wiki/ArmaLite_AR-15 under the paragraph "Scaling down the ArmaLite AR-10" - yeah, it's Wikipedia, but there are links to legitimate sites if you want to dig deeper.