there is no rule to use TE buffer, you can use DW.
it is better to use another liquid with the mix and that liquid if use for your samples and positive is better like DW because in this way you have highest similarity among your samples, neg and pos and this is the basic of use negative control.
Why does it use TE as negative control in qPCR multiplex?
The negative control in PCR or qPCR multiplex should be done to perform the negative amplification.
In my view, this negative control should be performed in the same conditions as the positive test: In particular the negative amplification mix is prepared with the same ingredients except the DNA template; in that case the amplification is negative compared to the positive one, so the positive fluorescence value and curves are effective and real ones.