But the definition of "reasonable" can be different things to different people, especially under these circumstances. What is reasonable to presume from behind our monitors means nothing. When you're in the middle of a firefight, your definition of reasonable can be a little more flexible.
One problem that we have here is a lack of context. Perhaps these solders were just in a fight the day before with a very similar van. Perhaps instead of presumed medical personnel it was more enemy fighters. If they didn't have clear markings, then it could be very hard to make quick decisions. This is the type of stuff that you just aren't going to be able to tell from a single video.
That is the "missing" context for you...
I believe that this video sets a very powerful context. Don't be ignorant!