That has nothing to do with the topic and I've never mentioned it in this thread.
I don't know where this quote is from, but DND Beyond cannot find it in not just the DMG, but in any 5e D&D book in it's database. I even cut up the quote into parts to try and find it that way, and nothing. It does not appear in the current 5e DMG as far as DND Beyond is concerned. The guidelines also never mention a party of four. They explain that the guidelines assume a party of 3-5, and give rules for less than three or more than five PCs, but never say four is assumed to be the standard and I did an extensive DND Beyond search for any variation I could think of on that phrase and never found it appearing.