Gematsu is a very weird topic in the Smash community. It's something that has alot of mystery surrounding it. It got alot of the characters right, but still had alot of inconsistences like Robin, Duck Hunt, etc. The thing is, Sakurai probably considers at least thousands of characters everyday and probably planned a couple for Smash 4 that didn't make the cut. That being said, I believe the reason Chorus Kids and Chrom were specifically mentioned because they probably were in development at one point.
If you look at the Chorus Kids, dataminers (Source Gaming A.K.A @
PushDustIn
) found a Rhythm Heaven icon in the characters folder of Smash Wii U. That makes me think that they had to be in development for quite sometime and were scrapped very late into development.
As for Chrom, he does have a model in the game (even though it doesn't mean anything) and his trophy pose could potentially be a render as it is a fighting pose (not really a good reason either, but trying my best
). So that's why they were maybe featured in the leak.
That's just my guess though. I'm really horrible when it comes to explaining things (and coming up with good reasonings), but I just wanted to get my thoughts out on the whole thing XD.