Welcome to the forum! It is indeed blocked by the density rules the community has observed. Not alone is not not alone in the red box outlined here, there are 2 pokestops in that cell already - there normally would only be one. I am guessing that a location edit has been made to move one of the others here:
For more details about the rules, see this topic: Why an accepted Wayspot may not be used in Pokemon Go (S2 cells and Pokemon Go)