Thoughts on what the X-37B was doing in space?
space.com
space.com
The biggest events were the changes in orbit, and that was probably mission control testing positioning thrusters and associated systems to prove the craft is capable of dropping in and out of a geostationary orbit and repositioning itself into different orbit patterns with ease + accuracy (and probably with little human involvement).
Given the craft hasn't passed a test of re-entry nor an automated landing from space, it seems unlikely the US Air force would have loaded sensitive + expensive monitoring equipment onboard, nuclear weapons or any of the other conspiracies - on this initial trip anyway.
They might have some scheme cooked up for refueling spy sats, which would extend the service life and give them the ability to shift orbits more freely. Still... even then, would it really be cheaper than lofting a new one?
In theory they could fit a guy in there, barely. That might make some sense for repairs. Assuming you could find a good mechanic without a trace of claustrophobia. And assuming the flight profile didn't flatten him. Maybe some kind of teleoperated repair bot?
Maybe you could fit someone inside, but that might just be the hardest mission ever flown.
As for the overall mission mandate may directly or indirectly be related to prompt global strike, a kinetic kill system (either for satellites or for ground targets), or electronic warfare.