I clearly see a kappa on the die, and kappa had a numerical value of 20 (iota having a value of 10). It also clearly has the first five letters in the Greek alphabet, which are 1-5.

If they're not using digamma or qoppa, however, they're generating 1-5, 7-9, 10-80, and 100-400 (likely) if they're numerical. It's more likely meant to represent the letters of the Greek alphabet, but I'm not clear how they decide which ones not to include. They might have just shown the first 20 (leaving out phi, chi, psi and omega), which would make sense if it was being used for instructional purposes - 20 sides, 20 letters in order. They could also have tried to leave out letters that were considered to be compounds, like xi and psi (k+s, p+s), but that still leaves them with 22 so I don't know what other 2 letters they could cut. I would say eta and omega, being longer values of epsilon and omicron, would be cut, but eta is clearly visible in one of the photos. Also, taking away aspirated versions of letters (like theta as a form of tau or phi as a form of pi) would be an option, but again, I see theta on the die in the photo.

It's most likely just that they decided to "number" the sides the same way that we sometimes "number" clauses in a contract: a, b, c, d, e, etc. In that case, the likelihood that the die is meant to generate random numbers or letters is very slim.