Japanese foam glass cup

This cup is 3.5" long x 3" wide x 2" high and has its original label but is otherwise unmarked. It was sold to me as a sake cup, but it seems quite large for that purpose. It has a recessed pontil which appears to have been worked to smooth it. It is fairly heavy for its size at 6.6 ounces.

It was on an online auction site for quite some time and I had made a couple of offers on it but they were declined. I finally repeated my lowest offer after several months and it was accepted. Calling it Japanese art glass as I am not yet certain what it is supposed to be.

The label says:

"Handmade
Oval Small Bowl
Foam"

Tea bowl? Dunno!