IT simply states the resolution of the DFT: each data point of the DFT corresponds to a a flat top, constant width bin whose height corresponds to the DFT value.
I think they meant it acts as an spectrum analyzer from the point of view that sets its values according to evaluation in each frequency "pass-band"  (in an spectrum analyzer the signal spectrum is built from taking the signal frequency content from small frequency pass bands, and then sweeping the central frequency of such narrow pass bands)
In the case of the DFT the pass band is replaced by the frequency bin.

Best
Tosei