The not-going-out-if-you-don't-have-to thing would probably be diagnostic of depression in 99.5% of the population...
However, with someone with an ASD, I would check for other symptoms or changes. Apathy, flat moods, lack of interest in hobbies, sleeping a lot or too little, negative thoughts, loss of apetite, loss of libido, etc, etc.
As
Sora said, if you used to go out more (when you didn't have to) and liked it, that might be a symptom. I don't go out much unless I have to or it's to do something specific, and even then I have to gee myself up. I am a total home bird and love my four walls. I might look like a depressed hermit, but I'm not; I'm a content one!
I think AC132 has summed it up.Another point is that most of the population don't know how
to deal with someone who really has depression.The person should be given positive support rather than simply being told things like "Pull yourself together" or "You've got depression" !