Me: Both an apples and an orange are fruit.
You: OMG did you just say that apples and oranges are the same thing?
Me: No, I just said that those two things belong to the same category because they have one trait in common - both grow on trees.
Me: Humans and animals are both sentient and deserve moral consideration when considering whether they should be exploited or killed.
These are two objects. The green object is an animal with all the traits animals have. The yellow object is a human with all the traits humans have.
People think that vegans think that humans and animals are the same.
But actually vegans think that humans and animals share a trait - sentience. Sentience is the morally relevant trait to whether or not we should exploit and kill somebody for unnecessary reasons.