Mammals are animals that feed their babies with milk. Humans are included in this category too. However, you won't find the emojis of people here — the author placed them in a separate block. Well, he did that probably because of the enhanced feeling of self-importance. If the list was compiled by a pig, all its snouts would be demonstrated on a separate page too.
Remember: the key thing that differs a human from a monkey — the ability to copy the emoji of a monkey.