Can complex envelope be writen in the form of quadrature components when it has symmetric spectrum?
The noise is actually never upconverted, it was already there in the bandpass channel. The textbook is simply modeling the noise as a quadrature signal.
To recap:

The transmitted passband signal is usually assumed to be noise-free.
The passband signal is real, and it occupies frequencies from $-W_2$ to $-W_1$ and from $W_1$ to $W_2$.
The receiver adds noise to the signal, usually in the first few stages of the analog front-end. This noise is passband: it occupies the same spectrum as the received signal.
The passband noise goes through the quadrature receiver and its complex envelope is calculated. In the process, the spectrum from $-W_2$ to $-W_1$ is discarded, and the spectrum from $W_1$ to $W_2$ is shifted to baseband.
As a result, the spectrum of the complex envelope of the noise is not symmetric.
In conclusion, we can think of the passband noise as a quadrature signal.

Here's an illustration: