No, it doesn't definitively say the backing storage is not tape based. Only that:

    "Essentially you can see this as a replacement for tape," 

and:

    "inexpensive commodity hardware components"

Nowhere did they explicitly deny that it may be tape-backed.

In addition, From the article:

     Instead, Glacier runs on "inexpensive commodity hardware components", he said, noting that the service is designed to be hardware-agnostic.

Which may allude to the fact that the backing storage itself may be flexible (a combination of HDD, Tape, possible BDXL)

The author himself only acknowledges:

    This suggests the system will be based on very large storage arrays consisting of a multitude of high-capacity low-cost discs.

Which isn't definitive in the slightest. Also, the article is over 18 months old.

I've said it before, I wouldn't be terrible surprised if they got started with old commodity hardware to get started, but the economics and characteristics of tape still seem much more amenable to the use case.