To state that disbelief is not a specific belief concerning something... is simply not true. To disbelive is to believe that something is not true. (-)A=B is the same as A=(-)B... you should have covered this in elementary school.
If you specifically DO NOT believe in something, without any proof or evidence to support that belief, then you are in fact BELIEVING that something does not exist.
Yes, I do not BELIEVE in Santa Clause, and that is not a component of my overall set of beliefs regarding the supernatural and paranatural that are broadly catagorized as "Christianity". It is not a component of my personal religious (definition of religious: relating to or manifesting faithful devotion to an aknowledged ultimate reality or deity) beliefs - which is the definition of "religion". Unless someone worships Santa Clause as a deity or believes that Santa is an aknowledged ultimate reality... it would be hard to determine that believing that Santa does not exist is a "religion".
If you want to examine that one specific article of my personal set of beliefs, I feel comfortable that there is not sufficient evidence for me to BELIEVE that Santa Clause exists. Therefore, I BELIEVE that he doesn't exist. While it would be foolish for me to call my lack of belief in Santa a "religion", it does fall comfortably within my overall BELIEF structure based on reality, which some refer to as "empiricism", while others think of it as "science".
As an illustration of something that is not a belief: I UNDERSTAND that evolution is the means by which life has come to exist in its current diversity - because there is sufficient evidence to justify that as an explanation, and it is in fact the best fit/least complex explanation that fully encompasses all the data we have at hand. All other explanations are more complicated and are therefore eliminated by use of Okham's Razor... So evolution, and gravity, global warming, the conservation of mass and energy, the supply/demand dynamics of free trade, and many hundreds of other issues... are intances of UNDERSTANDING or KNOWLEGE. But even these are based on a BELIEF in science and the underlying truth of what is seen and experienced - Descartes ending of the speculation of the caverns of Socrates.
To paraphrase myself, Harris is an idiot. Not believing in astrology is one of many personal beliefs that comprise my set of personal beliefs - which fall into the broad catagorization of "Christianity".
If you have no evidence to support your conclusion, then it is purely a statement of belief. Period. If those beliefs concern the realm of the religious - including sets of belief that state there are no deities - then those are still religions. Period. Atheism is a religion because it is an unproven set of beliefs concerning the aknowledged ultimate reality.