That is the Telegram channel in question. Surprisingly it looks so legitimate. I'm not sure what to think anymore.
Perhaps some dude registered on that channel and tried some shenanigans.
The thing is, more that one attempt to get support lead me to become suspicious.
What is your opinion of the channel at first look? Try them out with some questions perhaps.
It seems that mynodebtc.com is legit but the problem if you are talking about a random guy on their telegram support.
That's suspicious if they ask related to your private keys because it is supposed to be secret and you should be the only one who knows your private key.
Even if they are a support on "mynodebtc" you shouldn't share this key with anyone. Please be careful I believe the guy you talking to is not a mynodeBTC support.