Oops, sorry my bad. Honestly, that was a typo; I knew about Moody. I meant one of the other three.
AFAIK, Moody remained on the boat deck after Lifeboat #15 was lowered to the A-deck and so, he could not have been the "someone" in charge that Rule saw when he went down to the A-deck to meet the lowered boat. It could not have been Murdoch because Rule knew the First Officer going by the former's earlier statements and in any case, Murdoch had crossed to the port side by then. If we tie Rule's statement with that of Barrett, the man in charge could have been Nichols. Barrett said that Nichols was there (Ulster Echo) and ordered the Leading Fireman into Lifeboat #13 and 'pull an oar'; after Lifeboat #13 was launched, Nichols could have remained there just as #15 was lowered to the A-deck.
Unless of course, it was McElroy. I am still unable to figure out the Chief Purser's whereabouts during the activity around Lifeboats #13 and #15. But to complicate matters further both McElroy and Nichols were on the Olympic, as was Samuel Rule.