"You are outside a burning building and are told that inside one room is a child and inside another is a painting by Picasso. You can save one of them. To do the most good, which do you choose?"
The point he's trying to illustrate is that, if you knew for certain that you could turn around and sell the Picaso for millions and use that money to purchase malaria bed nets, the expected number of lives saved by using the Picaso could be hundreds, and so there's a moral dilemma present.
Like many hypothetical questions, this one feels a bit "off" or "unrealistic", but if you don't get hung up on the oddities, I think one can sense the essence of his question, and it reminded me of the point you're making here as well as a responder's question asking you why you think the way you do.
I do think these questions are hard for us to wrap our heads around -- how to value high probability immediacy against somewhat uncertain non-proximal/non-immediate things that might be "much higher value". Part of my human brain goes splat when I try to weigh these things.
In terms of the moral dilemma with the painting, I do have quite a bit of sympathy for the argument that one should do what they feel will produce the most good, which might be to save the painting and purchase malaria nets. My father on the other hand seemed to believe that to be absolutely morally wrong, which seems to be siding with your sentiments. Practically speaking, I think I'd almost certainly save the child's life, because one's human impulses would be so strong that they would override any high-and-lofty-rationality, and one wouldn't have time anyway to do deep analysis. But the question in a hypothetical sense does seem quite valid and hard.