The point is not that anyone would mistakenly believe that Digital Subscriber Line was the correct interpretation of DSL in that context. The point is that the nature of human cognition is such that Digital Subscriber Line is the term most likely to pop into consciousness first and it will be the wrong answer. The abbreviation DSL is not widely recognized as meaning Domain-Specific Language, or at least not so widely known that one may reasonably assume that any practitioner in the field will immediately know what you are talking about. They'll know that Digital Subscriber Line doesn't fit into context, but they won't necessarily know what meaning the author was trying to convey.