Neither TDA nor RRoP ruleset mentions anything explicit about how to handle a hand which is tabled by someone other than the "correct" player.
For the purposes of argument/discussion, let's talk about IWTSTH. It is worth noting that IWTSTH in TDA rules is much, much different than in RRoP.
TDA:
Quote:
18: Asking to See a Hand
A: Players not still in possession of cards at showdown, or who have mucked their cards face down without tabling, lose any rights or privileges to ask to see any hand.
B: If there was a river bet, any caller has an inalienable right to have the last aggressor’s hand tabled on request (“the hand they paid to see”) provided the caller tabled or retains his or her cards. TDs discretion governs all other requests such as to see the hand of another caller, or if there was no river bet. See Illustration Addendum [adopted 2013].
RRoP:
Quote:
Any player who has been dealt in may request to see any hand that was eligible to participate in the showdown, even if the opponent's hand or the winning hand has been mucked. However, this is a privilege that may be revoked if abused. If a player other than the pot winner asks to see a hand that has been folded, that hand is dead. If the winning player asks to see a losing player’s hand, both hands are live, and the best hand wins.
In TDA, to ask to see a hand, you must have made it to showdown, and either still be holding your cards, or have tabled them. And you can only ask to see the hand of the last aggressor. Any other request is at TD discretion only.
None of these elements are true in this hand: seat 8 has no cards (he mucked them just prior, and therefore has lost "any rights or privileges to ask to see any hand"), and seat 7 was not the last aggressor (ostensibly, since seat 6 tabled first, though I guess we don't know this for sure from the OP). The TD certainly did not use his discretion to force the hand to be tabled.
Furthermore, TDA rules make no mention about whether such a hand (tabled as a result of the request of another player at showdown) is live or not, and do not make any distinction between the current winner making the request vs. any other eligible request. [My contention is that they should be governed by Rule 14, and treated as live cards in all cases, though others may disagree.]
RRoP is different. It includes no discussion about what hands are live at showdown, is explicit that players must protect their hands (even though cards speak), and has an explicit IWTSTH rule which would make a hand dead if a non-winning player asked to see it. Though it's maybe a stretch to get from "a player turned over someone else's hand" to "that player is making a de facto IWTSTH request" as opposed to "that player is tabling a live hand".
RRoP was also last updated 10 years ago, and is not keeping pace with the modern game or customs.