He claims he was wrongfully denied access to those SAPs and CAPs, that is, he did have clearance and need-to-know status.
That is, "he
thought he had clearances as a UAPTF investigator". The first part of your sentence does not logically imply the latter without making further assumptions on Grusch's subjective
claim of having the clearance and need-to-know to these SAPs being objectively the case. A somewhat uncritical belief in his claims due to his former DoD position and overall demeanour is the crux of the issue here.
It makes sense with the clearances, because he was in charge of the Presidential Daily Brief previously.
There's a lot of simplistic Hollywood-inspired myth and misconception being bandied about when the public and even the politicians discuss the way security clearances work.
Speaking from my own government and defence experience, in modern militaries and government agencies an official's security clearance level concerns the maximum security clearance level to classified information s(he) has been granted (1)
on a need-to-know basis and (2) with regard to
a type of classified information necessary for the discharge of their specific assigned duties. In other words, you may boast the highest security clearance level available whilst remaining legally forbidden to access even lower level classified information which is unrelated to your mission / assigned tasks. You can also be deemed
untrustworthy and a
potential leaker which may become apparent from your belief system (say, an unwavering belief in secret alien recovery programs coupled with a resolute mission of uncovering all such government secrets).
For me to repeatedly state the above shouldn't be regarded as outrageous, disrespectful nor radical in any way, but rather as a rather predictable way a professional military apparatus works.
Suppose Grusch, as a UAP investigator within a DoD fringe entity (UAPTF) established by congressional pressure (initially campaigned by Reid at the request of Robert Bigelow), is asking questions about a classified program that concerns the recovery and analysis of advanced Chinese balloon technology but which he doesn't know is concerned with said Chinese technology due to the program being classified. He interviews a fellow UFO believer who has had marginal contact with aspects of said compartmentalized program, say, as a driver of officers to and from the recovery/analysis site whilst having no access to the high clearance core premises of the program nor being apprized of its exact nature. This interviewed fellow believer is convinced the Chinese balloon program is in fact an alien craft recovery program. The relevant DoD commanding officers working with said program would not only have every legal right to refuse Grusch access to this program, but to complain to their chain of command about a person within the DoD sniffing around programs he should not be concerned with.
In order to protect this driver from further repercussions, Grusch may withhold naming names indefinitely.