based on the timing that calhoun left, there was only 4 options as far as i can tell:
1) name an assistant other than ollie as interim coach, making it clear that ollie is not a candidate and then perform a national search in the spring. this is probably a non-starter, as it would piss off more people than it is worth between calhoun, ollie, and the fanbase.
2) name ollie interim coach, with a chance to compete for the position in the spring. this option doesn't instill much confidence in ollie, tags him with the dreaded "interim" label, and probably pisses off calhoun anyway.
3) ollie gets 1-year contract. to me this option is hedging between giving ollie a vote of confidence, and trying not to piss off calhoun. i understand the move politically, but it leaves the program in a bit of limbo because there is no clear way to establish success parameters for an extension, outside of the extremes. like if ollie wins 25+ or wins less than 5, both of which are very unlikely, the middle is nothing but gray.
4) commit to ollie and give him a real contract. to me this is the most logical choice, it keeps calhoun happy and likely keeps him around to at least help guide the program through conference realignment. ollie gives the best shot at some continuity, and what is the worst thing that can happen; basically that he stinks and you fire him and start over anyway.
in summary, i think the one-year contract was an olive branch to try to keep calhoun happy, and may be a safe move unless ollie turns out to be mediocre and manuel doesn't extend the contract. the worst case scenario is that ollie does decent enough to not suck, and manueal decides not to extend him in which case you wasted year on ollie and still have a pissed off calhoun. in that scenario manuel should have ripped off the bandaid and gone for option 1, pissed calhoun off from the start, and then tried to win him back.