I think that "coverage limit" may an incorrect/confusing term in this case... his coverage limit should be $90,000 for all buildings and contents (all 3 buildings 'blanketed' together), but the loss was only for $60,000.  Therefore he was fully covered for, not limited to, $60,000.  He would not receive $90,000 for a $60,000 loss, but he could receive up to $90,000 IF he suffered a $90,000 loss, whether in one building or more.

Jean is correct that if the buildings had separate limits, then even if the insured had stored $60,000 of contents in one building, said building only has a coverage limit for $30,000, therefore he would only receive $30,000 for a $60,000 loss.

If I am incorrect in this, PLEASE let me know, as I am taking the final soon :)

I am basing my answer off of the info. from the state manual, pg.35.