i don't think he ever gave us a full explanation but he did mention the nickname again when he was on live from his new bedroom, talking about his new mattress! so i think it's just a play-on-words and he thought it was cute and reminded him of mtw. which honestly, for a T, that is especially endearing that the man who has everyone saved so formally decided to put a cute nickname for matthew (and only matthew). he also has yujin as "maknae yujin" but that's less of a nickname and more of just an addition to the name. 😜

this was like a year ago too and him and mtw are even closer now, so i'd LOVE to know if that nickname has been updated 👀 maybe to one of the newer nicknames he calls him (jagiya, honey, sweetheart, wife)........ it might be wishful thinking but i don't think the possibility is zero 👀👀