This is tribute to D&Ds deck of many things, which can give you amazing rewards or royally mess over the campaign. I think blizzard captured the feeling of that magic item perfectly in the RNG high risk high reward of this spell.
I agree not clear. My guess is that YOU cast this card, and THE CARD casts a random spell. So the casting of the card itself would proc Quest, Yogg, Flamewaker, wyrms, etc., but the casting of random spell would not.