Regarding the validity of whether or not Rebelskum was actually threatened, it really comes down to how it feels to discuss defamation with a high-ranking military official and a non-physical, indirect definition of ’threat'.
Rebelskum said "It's not every day that a Lieutenant Colonel who specializes in counter-intelligence and psychological warfare drops a line in your inbox” and “It was a bit intimidating for an average joe like myself.”
After an email to RebelSkum, I was able to get my hands on some screenshots of the exchange he had with Mr. Aquino from May of last year.
Rebelskum prefaced the screenshots by saying, "It would be difficult to describe our conversation as an outright "threat" but once the word "defamation" starts getting thrown around you can easily guess where's that conversation is headed.”
In the email, Lt. Col. Aquino states how he had “recently come across and extremely defamatory page” on the pizzagate wiki and asked Rebelskum “do you know whom I might contact to correct defamatory material on the site?"
So, this wasn’t a physical threat or anything, but the legalese invoked by Mr. Aquino would be enough for anyone’s pocket to indeed feel quite threatened.
"I was playing it off as politely as possible. I figured if I appeased him quick enough he might stop trying to edit content and escalate the situation, especially considering he didn't know I was the actual owner of the site and he literally wrote the book on psychological warfare. All things considered I didn't have any resources to counter any litigation and was already dealing with attacks on several of our pages already on top of my own personal problems.”
Just in case there’s any uncertainty of whether this was Aquino, in this email he references his writing,
https://xeper.org/maquino/nm/PSFSummary.pdf
a link to his books
https://www.amazon.com/michael-a.-aquino/e/B01GEWRIMU
as well as an overview of his experience and qualifications
http://www.rachane.org/docs/AquinoVitae.pdf
Some further email correspondence screenshots between the two can be seen below.