Well, they apparently haven’t logged into their main since the Shadowlands revamp seeing that the character is still level 50, but they did list the name of their main:
Minotaur - Achievements (worldofwarcraft.com)
Mynogra - Achievements (worldofwarcraft.com)
^ More than enough achievement overlap to reasonably assume they are telling the truth about the pally on Proudmore being their main. Generally, people that constantly refuse to post on their main are always full of it from my experience, but I know that there is precedent for characters not showing up if you haven’t logged into them at least once following a major X.0 expansion related patch. The fact that they’ve given the name/server and the achievements match shows they aren’t lying about that at least.
All that being said however, I always take every “I’m deleting my account!” post with a massive grain of salt. I could see quitting for a time and coming back later (I’ve done this myself several times for various reasons), but anyone saying they are totally deleting the account is typically going to let the sunk cost fallacy stop them.
https://tvtropes.org/pmwiki/pmwiki.php/Main/SunkCostFallacy
https://en.wikipedia.org/wiki/Sunk_cost
The short version: you can’t get the money you’ve already spent back. Sub time isn’t refundable, and a license key can’t be traded back to Gamestop. In the event that something happens to make you want to return, you’ll be 100% back at square one and having to purchase everything again. At least by simply canceling the sub and keeping the account, you can mostly pick up where you left off if something happens and you change your mind later.
That’s the reason why I’ll never believe a “I’m deleting this account!” post/threat over a simple “I’m quitting” post.