It took me a while to figure this out, and I'm not sure that all physists are aware of it; maybe we should explain it in that paragraph?
Also, the notation Ψ = Ψ(r,t) seems to imply that the Hilbert space is the space of square integrable functions, but that is only true in some special one-particle examples. Often, the Hilbert space is a tensor product of several finite- and infinite-dimensional ones, and the elements of it cannot really be thought of as "wave functions" (which is why I quoted that term in the original article). --AxelBoldt