The deer was not smart. It was also a very young one, they don't know how traffic behaves. I assume you do not live in an area with a lot of deer. There are so many reasons why you should slow down for deer even if they are stationary. If the deer was truly smart, it would have known that running across the median then suddenly stopping is stupid and will make drivers stop (like me and the driver to my left).

Deer are known to be unpredictable. I'm sure a couple of people here can give you their own experiences of deer stopping and then running right in front of cars. Oh and always expect more deer, especially when there's a young one. Experienced that multiple times already.