I'm really torn on this one.
The argument that the only reason to specify "bard" instead of "sorceror" is to add the "no arcane spell failure chance while in light armor" is very compelling to me. Assassins also have light armor proficiency, which is something the bard has and the sorceror does not. It doesn't make a lot of sense to me to give the class proficiency in light armor and then make their spells harder to cast because of it.
However, the argument that the other bard rules for casting a spell, with it's focus on verbal componants, is also compelling. You shouldn't be able to pick and choose which elements of bardic casting you carry over, if the class is going to be unspecific on the subject.
I suspect this needs errata. The errata should specify that they can cast spells spontaneously, and suffer no arcane spell failure chance while wearing armor.