It's hard to judge because there may be more to the dynamics between them that what we know.
At face value I think he was wasteful but not rude, because I find unacceptable to act behind other's backs - with exception for the case when it's the only way to pursue a right.
A small piece of food isn't worth being false or risking the harmony in the house. Besides she could have compromised eating it herself rather than throwing in the pan for everyone.
She sounds like a person who is going to follow her way with little consideration for boundaries. And the guy, failing with words, is at loss for some other way to escalate his argument.