The system is one the tourists are trialling in their white-ball series in South Africa, having cleared the use of the coded messages with the match referee and anti-corruption officials.
"Nathan is the analyst of the Multan Sultans in the Pakistan Super League - he said the idea was live signals to the captain, who was Shan Masood.
Athers added: "A lot goes on at the end of a T20 game - there was a blizzard of sixes here - so I'm not sure Morgan would have been looking too far up at the balcony!"
Sky Sports Cricket expert Michael Atherton sees no problems with England's idea and said he spoke to Leamon about it during lockdown after he initially trialled the system in the Pakistan Super League.
Speaking after England's thumping nine-wicket win at Newlands, England vice-captain Jos Buttler told Sky Sports jokingly: "[Leamon] was calling out the EuroMillions numbers - the lads were checking their tickets!
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The signals for Morgan came amid a blitz from South Africa batsmen Rassie van der Dussen and Faf du Plessis, with the duo pummelling 84 runs from the final five overs as the Proteas posted 191-3.
Michael Atherton assesses the signal system England are trialling with analyst Nathan Leamon offering captain Eoin Morgan information from the balcony
The England and Wales Cricket Board said the signals were "intended as a live informational resource that the captain may choose to use or ignore as he wishes" and that "they are not commands or instructions and all decision-making takes place on the field".
"Seriously, analysis has become such a huge part of the game
"It was about offering him information, which he didn't have to take.
"Eoin is one of the best captains in the world, a fantastic, instinctive captain, and there's a nice balance going on
Last Updated: 03/12/20 2:04pm
Morgan (left) can use Leamon's signals as he sees fit or choose to ignore them completely
"You have to be careful how you use the information best - there still has to be an instinctive, intuitive side to the game but if you can use analysis to better that then it is a force for good."
England analyst Nathan Leamon had placed a series of numbers and letters on clipboards on the team balcony to give Morgan suggestions on how to impact the game from in the field.
"I am okay with it. It is very different to Bob Woolmer feeding stuff in real time to Hansie Cronje in the 1999 World Cup through an earpiece."
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England subsequently cantered to their pursuit of 192 for 3-0 for a series sweep, with Dawid Malan (99 not out from 47 balls) and Buttler (67no off 46) smashing an unbroken second-wicket partnership of 167 in 85 balls as the tourists eased home in 17.4 overs.
"I don't think Eoin needs too much help when he is out there, he is a fantastic captain, but he works closely with Nathan to come up with suggestions and certain match-ups. It was an offering of help. It's just a little bit of an experiment.
"I think they were doing hand signals in the PSL, whereas here it was slightly different.