If it has been sitting for a while, it's very possible the lifters are no longer pumped up, which makes the duration at the valve much shorter....... And the compression test will read high.

If the 250psi had been observed just after the motor was run and warmed up, and you knew the gauge was accurate....... Then I'd say the cam was like a tooth off(advanced), or the motor is way over 10:1cr(as in waaaaaaaaaaay over).