My milk vs Mrs. cow's milk

For ages, every time Aga saw me feeding Lila using expressed breast milk in a bottle, he ALWAYS, ALWAYS said "Mommy Aga wants it... Aga wants sister's milk...". I kept telling him "No no. This is not your milk... Trust mommy, your milk is much nicer than this. This is bleh.. yucky. Not nice. Really." His milk is normal full-fat mother cow's milk.

On the n'th time finally he insisted he MUST have it. I don't want him to cheekily drink Lila's milk using her bottle when I'm not looking, or exchange his milk with hers trying to feed her. Both are not allowed, so I decided to give him a taste of the medicine. I poured around 5ml of the expressed breast milk into his milk bottle and let him try it. Not a lot because I was expecting him to agree with me immediately that his milk tastes better. You should have seen him, his eyes were glittering with excitement when he saw me doing that. I bet he's thinking, "Finally! This woman finally let me have that delicious milk!!!"

When he had one sip to taste, I could see from the expression on his face that he DID NOT like it, at least he DID NOT expect it to taste like that. He thought it's sister's milk so it must be NICER!

Me: Not nice, right, Aga?
Aga: (pretending to smile) Nice. Very nice. (still had that strange facial expression, though)
I laughed my heart out. Poor kid. He didn't want to admit that he was wrong! :p

I saw him finished that 5ml (he was struggling to finish it albeit very little), and asked him if he wants more because it's so very nice. He hesitated for a while and then said YES. I had to confirm twice if that was really what he wanted. He still nodded saying yes. What a stubborn kid. Just like his father.

With the young master's order, I poured a little bit more this time, around 20 ml. He wasn't as excited as before, and struggled more to finish it.

Aga: (searching for his bottle cap) That's it Mommy, I had enough.
Me: Oh, you said it was nice. How come you did not finish it?
Aga: Noooooooo.. it's NOT NICE!!!!
Me: But you said it was nice.
Aga: No. Not nice. Poor sister. Her milk not nice.

I was laughing, but as he said the last sentence, it tickled me. Should I take it as an insult - that Mrs. Cow's milk tastes MUCH better than MY milk? MY MILK??? Think about it. Why does human like cow's milk better than human's milk? Strange but true. Dare to think the opposite? Would baby calf think human's milk tastes better than mother cow's milk??? Mother cow must be so blessed. Her milk is much preferred than human's milk, and on top of that, she could feed all her kids with her milk and STILL has enough milk to feed us all. I dare not to think the opposite. God bless mother cow!