This is a debatable whether it was RDM or not. As for it being RNT that is not even a rule, you are allowed to throw grenades in quite a few situations as long as they are not thrown randomly towards players for no reason. As for throwing grenades thru the portal, i would advise you not to do this even if you did watch someone go into the t room and are hoping to kill them, this is because it is difficult to know who is in the nether at the time of you throwing a grenade and you could end up killing someone who you didn't mean to. For example even if you had a radar and saw only one life in the nether you might assume that they are the traitor who went into the t room, or they could just be an innocent who was in there already. You get my point, dont throw grenades where you cant see who it will hit.

This is a debatable whether it was RDM or not. As for it being RNT that is not even a rule, you are allowed to throw grenades in quite a few situations as long as they are not thrown randomly towards players for no reason. As for throwing grenades thru the portal, i would advise you not to do this even if you did watch someone go into the t room and are hoping to kill them, this is because it is difficult to know who is in the nether at the time of you throwing a grenade and you could end up killing someone who you didn't mean to. For example even if you had a radar and saw only one life in the nether you might assume that they are the traitor who went into the t room, or they could just be an innocent who was in there already. You get my point, dont throw grenades where you cant see who it will hit.