AITA for serving myself the biggest piece of meat?

My boyfriend and I have been together for about 2 1/2 years. We live together as of recently (4 monthsish) and we get along pretty well. We have a lot of separate hobbies, and one of mine is hiking. I wouldn't call myself a "peak bagger" but I do like to add mountain summits to my hikes when I can. BF doesn't enjoy hiking more than occasionally so he rarely comes along.

For reference, I am a 5'3" 150lb woman. He is a 5'7 170lb guy.

On Sunday I went for a long, strenuous hike with my friends. If you're familiar, it's 13er James Peak in CO. It was a 9 mile, 3,000ft elevation gain hike (from where we started). I had a fun time and went home and did my usual workout (short run, weights, some light yoga) after. Suffice to say, I was pretty hungry by dinner time. I made dinner, which was grilled chicken with lots of grilled veg, some pasta salad as a side. When it came time to eat, because of my big day, I grabbed the bigger piece of chicken. We're talking a 5oz piece versus a 7oz piece.

BF got upset about this when he saw my plate versus hit place, and he made a pretty big deal out of it. He told me that there's no reason for me to serve myself such a big piece of meat, he's the guy and he should have it. I told him that I'd hiked and done my workout that day, and that he puttered around the house and went for a short (5 mile) run.

He told me that growing up, he was always taught that the man got the biggest piece of meat because men need more to sustain themselves in general. I said that I agreed, but again, I'd climbed a mountain that day and burned much more than he did. He told me I should accept the good calorie deficit, or load up on the pasta salad and veggies instead.

We've been arguing about this for days and he tagged some friends in and asked his parents (who said to keep them out of it, lol). So far people are split, some believe even if he didn't do much that day it's just weird for a woman to actively try to eat more than her boyfriend. I think that's stupid and outdated and comes from a time when men tended to do more physical labor in general.

AITA? Is this just really dumb?