This is typical of Google recruitment from what I gather. Of the calls I've had from Google (I clearly match some weird mix of keywords), only one involved a specific position. For the rest getting them to confirm the position was in London (in one case it turned out that, no, in fact, the position involved Trondheim, Norway, and I'd been approached because I'm Norwegian, and they thought not to mention this until I asked for specifics) is about as far as they'd go. [I always push for position because my languages means I frequently get approached by cagey recruiters trying to get me to move to some god-forsaken place in Germany I have no interest in visiting, much less living in.]
Even nailing down whether or not my expected salary range was anywhere near what they could offer seemed a near impossible task (at least one recruiter said she didn't know as it'd be determined by a different team). I started pushing for this and rejecting the ones who couldn't answer, after I managed to get one Google recruiter to admit that my then-current salary was well above what they'd be willing to offer for the type of position he was hiring for (I didn't manage to get a proper job description out of him, though).
> I don't understand the concept of interviewing not for a job but for a slot in a pool of talent to be assigned only after I am accepted.
The hilarious part, to me, is that this is as old school as you get. E.g. the British Civil Service recruits this way. You apply to a department, say the Court Service, and is assessed roughly for a salary band, and interviewed. You're then put in a pool, and the recruiters work to place you in a specific position for the duration of your interview validity (12 months when my ex worked there). But the British Civil Service interview process is far more transparent and efficient for the most part than my experience of Google's.