Unless the loot rules were set as main spec > offspec, he/she does have a point in a PUG.
A lot of people run PUGs for offspec gear, and while that rule is commonplace, it's a courtesy rule rather than a god given right. It's more of a guild thing mainspec > offspec for me. You can expect that courtesy of your guild, but he/she's just another player trying to get the best for him/her.