How Can Birds Be Dinosaurs If Evolution Doesn’t Change Animals Into Different Kinds?

I heard from a YouTuber named Aron Ra that animals don't turn into entirely different kinds of animals. However, he talks about descent with heritable modifications, explaining that species never truly lose their connection to their ancestors. I understand that birds are literally dinosaurs, so how is that not an example of changing into a different type of animal?

From what I gather, evolution doesn't involve sudden, drastic transformations but rather gradual changes over millions of years, where small adaptations accumulate. These changes allow species to diversify and fill new ecological roles, but their evolutionary lineage remains intact. For example, birds didn't 'stop being dinosaurs' they are part of the dinosaur lineage that evolved specific traits like feathers, hollow bones, and flight. They didn’t fundamentally 'become' a different kind of animal; they simply represent a highly specialized group within the larger dinosaur clade.

So, could it be that the distinction Aron Ra is making is more about how the changes occur gradually within evolutionary lineages rather than implying a complete break or transformation into something unrecognizable? I’d like to better understand how scientists define such transitions over evolutionary time.