There are only a few abilities that Doomtrain has right from the start. Junk shop is the ONLY one that isn't used by any other gf, a talent is refered to something that is rare and unique, no one has the same talent in the same way.

I used the word talent to specify that it was not something that every gf had.

Every other ability he has, has to be learned, and needs to grow. Junk shop didn't, he already had it. Also most of the abilities leads to another, such as SumMag+20% leads to SumMag+30% so that is another form of growth. Junk shop does not do any such thing.