Well, its difficult to say why the osprey ignored the sparrow. Normally they are not fond of anyone coming close to the nest. And there is nothing wrong with a free meal either, even if they are usually fish eaters.
Again the comparison with the bald eagles gives good example: about 95% of their prey was fish too, but a few times they also brought a opossum, once or twice a bird (I assume a egret, but its hard to say since they were pretty messed up) and once a rabbit.
And there were also occassionally smaller birds landing in the nest tree, but they kept a safe distance to the eagles, and the eagles always kept an eye on them.
I find it fascinating that we now can learn more about the interactions between different species, thanks to the camera technology we have now. This way we can learn details of the behaviour, that was not known before since a human observer always disturbed the behaviour of the animals.
Things like what insects live underneath the eagle nest and what they do during the night.
And the best thing is, that everybody can participate in the observations, via the internet.