If you look at each of the 'objects' you will see they are quite uniform with longitudinal sections, all seeming to meet in the middle at the ends of the barrel shape. I think this suggests they are not caterpillar dung, so we have to look at possibilities.
It would be unusual for a group of seeds to be in a place where there are no plants.
The most likely answer is as you suggest, something which has come off the oak tree from above. What that something is, is the question.
The structure does look like something excreted, but as said the form is too uniform. It might help if we knew what sort of Oak tree it is, there are all manner of galls which are made by various insects, often wasps, although these don't look like a typical gall I don't think there is any such thing as a typical gall.
The other alternative is they could be some sort of vegetative material from the tree, I know the oak tree I have sheds catkins.
Maybe you could try breaking one up to get a better idea?
Looking at the one on the left, I can see there is 6 equal segments joining at the end. Looking at the one on the right, it looks to be open at the other end.
