I can't say ive ever seen that. I have about 10 of them atm and had about 40 over the years. They normally uncurl from the middle like a tree fern. Maybe its a mutation or something. Is that spagnum moss in the centre? Maybe spores have blown into the vase??? Do you have any Fishbone Fern around? I have some near mine and they look very much like A. Nidus for a couple of months before the fishbone sends out its true fronds.

Excuse Fern-Freak, for various reasons I could not check the forum until today.

Next to this Asplenium nidus there is only one plant of Phlebotium aureum, which otherwise has never produced spores.
What seems sphagnum at the centre of the rosette, is a fluff produced by the plant itself:
I do not think that they are young sporophytes of some species carried by the wind, before their appearance would have noticed the prothallia.

In these days when I have not been able to take care of plants the new buds seem on the point of wither.
I will continue to follow their evolution and if there is news I will update you.

Yes keep us updated. It'll be interesting to see what happens.
Take care
Tim