One of the benifits of SOA is the services are exposed in a technology/neutral manner to consumers.
But, as you have rightly pointed out, you cannot implement an SOA with a "technology agnostic" language or tool, since such a language or tool is difficult to imagine. In other words, you have to use some (or many) technology(ies) and then follow SOA pronciples and practices to implement an SOA.
The book uses Java (or specifically JBI API and spec) to do integration. To quote from the book:
ESB or JBI are not an end by themselves, but a means towards an end (which is SOA). An ESB is not required to build an SOA, nor is JBI required for ESB or SOA. However, all of them have something in common using JBI�we can build standard components to be deployed into ESB architectures. Thus, JBI by itself is one of the ways by which we can attain SOA.