Sounds like you got pegged at the border. In which case the CBP can pretty much do what ever they want (i.e. the 4th amendment does not apply) except as a citizen they can not deny you entry into the USA.
However, while the CBP can ask you for computer passwords you do not have to comply - that is true for any questions the CBP may ask you (i.e. the 5th amendment does apply). Not complying can lead to your computers and other electronics being temporally being confiscated - i.e. the disks copied for further analysis.
Here is a good primmer from the EFF:
https://www.eff.org/wp/defending-pri...igital-devices