No it is not. It is quietly assumed that the reader is experienced in RFID and similar technologies and understands the nature of the received data.

Basically, the circuit in question is a specialised narrowband AM transceiver.
The "signal" in question is simply noise of all kinds (IIRC, the u2270 amplifies the useful portion of spectrum by 120dB, it's quite a lot). Although in theory there might be some sort of squelch applied to the detector's output, it would hinder the circuit's operation e.g. in environment with ambient noise substantially lower than the squelch's threshold, where higher sensitivity (longer reading distances) could be otherwise achieved.

It is assumed that the noise will be coped with at higher level - as Per said, utilising the particular properties of data transmitted by the tag (e.g. checksums). This allows the developer to decide how to cope with noise: he can reject noisy data altogether, or he might try to develop algorithms capable of decoding valid data even in presence of some noise.

JW