[BlackFly]

You might be interested in this classic pdf: http://www.cs.virginia.edu/~evans/cs655/readings/steele.pdf (Growing a language)

Without those function names that you talk about, you wouldn't really recognize a language. Those standard library function names give the "batteries included" kind of feeling. The size of the community libraries furthers that accessibility and productivity feeling of the language. Furthermore, you can certainly create control flows via libraries--with callbacks specifically--and create any kind of novel branching structure your domain had need of.

A good API is a sort of DSL. If it well reflects how you think about the domain and helps you express instructions within that domain. The language can be very different. We experience that in our own language when we hear people talking with heavy use of jargon we don't recognize: they might as well be speaking another language.

But overall I agree with you that I would probably save the use of the jargon term DSL for novel syntax targeted at a specific domain.