Procrastination and depression are different from each other but some people who are depressed do procrastinate a lot.
Depression can lead to procrastination because when you're depressed you really do not feel like doing anything at all.
I know when I get depressed I'm usually almost always delaying or postponing something that I need to do or I'm supposed to be doing.
So I would say that procrastination could be seen as a form of depressed for some people.
However most times procrastination just simply means that the person isn't feeling like doing something that they should be doing.
Sometimes the person would rather be doing something else instead of what they were procrastinating about and it doesn't means that the person is always depressed.