No it isn't unethical. However it is a courtesy thing. Usually those that put on shows and competitions exclude themselves from being participants. This happens across the board, from marching band competitions at the high school level all the way to large corporate events and sponsors. There is almost always something in awards legalese that says "those that are involved in the event are not able to enter or win prizes". However it would sound like Shutterfest had no such terminology. If there is no terms stating this for the event, then there is nothing unethical or illegal about it. Again though, some might consider it in poor form. Others are most likely simply jealous, but it is hard to differentiate which is which.
The only thing that could cause an issue of dishonesty or unethical behavior would be where he states the judges didn't know his work from others. If that wasn't true, then his statement is a falsehood, and he certainly is being unethical. If the judges had no idea one photo from another and voted purely based on content, aesthetics and composition, and nothing was noted in the competition about whether he could compete, then I see no ethics breach here. It won't win him any friends though.
Also none of this excuses personal attacks and general bad attitudes on the web. Vote with your presence or support of the event, not with ugly venomous comments and threats, which seems to grow day after day on a number of issues. 2 wrongs won't make any of this right.
Reminds me of this that I have been told a number of times (probably because I am quick to comment on things): "A fool gives full vent to his spirit, but a wise man quietly holds it back."
I know I am happy with Godox, and so are so many others, one little article isn't going to make me sell everyting and spend 3x as much on some other lighting gear.