Hi, and welcome to the UK Fungi website.
The bracket fungus in you photo isn’t Oyster Mushroom, but one of the typical bracket fungi that grow on fallen decaying logs. (Possibly Turkeytail).
I’d suggest that the “white balls” are maturing fruitbodies of a myxomycete (Slime mould) which is growing on the bracket fungus.
It could be that the myxomycete’s plasmodium stage (which would have actively moved around, albeit very very slowly, looking for nutrients), might have been “feeding” upon the bracket fungus.
Once a myxomycete decides it’s time to fruit, (triggered by some chemical signal), the plasmodium loses the ability to move and morphs into the actual fruitbodies.
Those in your photo, being white, are fairly typical of the first stage of that process. – They will harden and change colour over the coming days, and when fully mature, will split open (dehisce) to release their spores.
Regards,
Mike.
