Your best bet in my opinion would be to review the books that the miniseries was based on. Those being: "With the Old Breed: At Peleliu and Okinawa" by Eugene Sledge, "Helmet for My Pillow" by Robert Leckie "China Marine" also by Sledge, and "Red Blood, Black Sand" by Chuck Tatum.

Sorry I dont know a more definitive answer off the top of my head, but I'm guessing the incident appears in one of those books, allowing it to be regarded as true.