That is certainly an interesting problem, one I first saw in a Hackaday post from a few years ago [1].
Personally, I've always wondered how any aliens would interpret the Arecibo message - if they could even decode it, that is.
I always thought aliens would think the marks on the golden disk are as meaningful as the defects on the semiconductor chips. I can't imagine why they would wonder if it's a message.
We get radio bursts from dying stars and try to interpret them as messages. Intelligence as we know it is pretty obsessed with trying to extract information from its environment, even where none may exist at all.
[1] http://hackaday.com/2015/10/06/electronics-for-aliens/