Interesting. I am never one to deny what somebody reports. I once managed a small factory. I always hated it when the foreman came in my office reporting something happening out on the floor that was totally impossible. I knew if i went out there, it would be just as he said and I would have to figure it out.
Air will leak out of a system where brake fluid never would. My guess is that under pressure, the air slowly leaks out. I have seen spongy pedal slowly get better on its own. I always though it was the air slowly working its way to the top.