I believe this is known as 'Lagswitching'.
I've seen someone using this before in a video explaining it but link was broken and this was probably years ago during beta maybe.
"These hacks alter network traffic to create latency. Sophisticated programs allow packets from the server to the client but delay or lose packets from the client to the server, allowing the hacker to experience fairly low latency gameplay while the server reports that the player is extremely laggy. These hacks are almost identical to actual network issues that clients can experience."
This is probably the best explanation i have of the program, it would most likely be a proxy, or something likely, most people haven't heard of this because this is probably the most intense way of hacking, or maybe someone wanted this for themselves.
I believe this is known as 'Lagswitching'.
It's not and i can tell you that with confidence, Lag switching either disconnects you, or hogs all you're bandwidth, pretty simple and useless, and i've never seen anyone experience low latency gameplay while lagswitching, it's just a stupid thought anyway. I'f you read my quote you can clearly see that it says it drops or delays outgoing packets, and the experience low latency is part is probably the server lag compensation for you, so you're not actually lagging but the server thinks so, just imagine that, seeing you're opponents 2-3 seconds before they see you and react much faster.