Why does the eldritch altar think that the mirror shard is the basic currency?

On the mystical altar, there is a property "(1.6–3.2)% chance to drop an additional Divination Card which rewards Basic Currency". Please note that we are talking about the BASIC currency!

To quote Bex_GGG: Basic Currency is a new term we've introduced that describes currency that drops randomly from normal content. As opposed to currency items that are specific to league content or things like the Awakener's Orb.

According to this information, as well as what is written on Wikipedia, we can safely say that the mirror shard is not a BASIC currency (it is the currency of the Harbinger League).

Attention question! Why eldrich monster drop divination card “Seven Years Bad Luck” (mirror shard) with the mystical altar mod for a chance to drop a divine card on BASIC (!!!) Currency (this happened on Plateau Map)?

Id like to guess, that it is because mirrors is a basic currency drop and therefor, the shards will also be considered as such.

err cause it's basic currency?