Yeah the ATF is a shit show of an agency with a strong history of fucking up in violent and unconstitutional ways - but unfortunately, their search warrant execution and 'raids' are completely standard operating procedure for US police.
It likely could've been resolved if they'd just sent him a letter asking to meet him at the Federal Building but who wants to be a desk jockey when you can play dress up like GI Joe?
Nobody gets promoted by making a phone call and telling their boss that nothing is actually in violation of law.
But kick a door down in your sparkling clean body armor and perp walk some guy who makes a quarter million dollars a year out of his mansion and you're well on your way.