I judge people who judge others for gatekeeping. God forbid I have a well informed and strong opinion based on experience. If I share that with a casual or new person then it’s now called gatekeeping.
It’s ok to have different opinions but not all opinions are equal, and if you’re a casual participant or new to a field/hobby/whatever your opinion doesn’t matter as much. Additionally, if you are discouraged and feel held back by strong opinions by others then maybe you should be kept out.
Their explanation sounds like ad hoc BS.