I don't want to speak for amishmanish again, but I'm pretty sure by "old guard" he means long-time members of bitcointalk. Amishmanish registered in 2017, so both Lauda and TMAN probably seem like they've been around since the beginning, even though they both registered in April 2013 (4 days apart, which I never realized....hmmm). Come to think of it, they might know each others' identities quite well.
TMAN traded on the forum quite a lot so his identity is probably known to some folks, particularly in collectibles. Not that it matters really. If someone leaves quietly and doesn't owe anyone, why would we need to know anything about them or the circumstances of their departure.