I'd almost say "introversion" or "selfishness" is the right term, if the latter weren't so prejudicial. You aren't collecting bus tickets or obsessing over infinite series to advance your own material interests or standing in the external world.

"Disinterest" doesn't work at all in any sense of the term. In the absence of overt mental illness, the bus-ticket collector must see it as being in his best interest to spend his time collecting bus tickets, or he'd do something else instead. ("You are your calendar.") The search for gratification, however externally meaningless, is certainly a valid expression of self-interest.

Put another way, if you would object if you were forcibly stopped from pursuing a goal, then you cannot be described as "disinterested."