I don't know much about him? Anyone care to elaborate.. The timing does seem rather 'fortuitous.'
About Matt O'Connor? He was a league convert from Australia, played center, had one Wallabies test, played and coached in Japan. Most recently, he was an assistant coach at Brumbies in 2007, and in 2008, he was brought in as a backs coach for the Leicester Tigers when Heyneke Meyer was their head coach. So if you know how Leicester's backs played between 2008-2012, you have a sense of what MOC might bring.
He was appointed coach at Leinster in 2013 when Joe Schmidt left to take over the Ireland job. This coincided with Johnny Sexton leaving for Racing Metro and Isa Nacewa returning to New Zealand, as well as Brian O'Driscoll and Leo Cullen's final years, so MOC was dealing with a team on the down-swing. Leinster was already known for being attacking sorcerers under Schmidt, and what MOC wanted to bring was a water-tight defense. Their defense did improve in 2013, his first year, but their attack started to slow and stutter, and their try count started to drop. They went out in the Heineken Cup quarterfinals to Toulon, but managed to win the Pro 12, beating Glasgow in the finals.
This year, though, everything seemed to go sideways. There was a problem at 10: Kiwi Jimmy Gopperth was his preferred starter for being more trustworthy, but Gopperth rarely brought much incisive attack or creativity. Ian Madigan could bring the flair at 10, but wasn't the most stable player in that position. The Ireland national side, I think it's fair to say, would have liked to have seen Madigan get more time at 10 so he could mature and develop some stability, but instead MOC put Madigan at 12, and had him coming off the bench -- which was strange, because Leinster had a great up-and-coming 12 in Noel Reid who needed seasoning and wasn't getting it. Johnny Sexton is returning to Leinster, so barring injuries Madigan isn't going to start at 10 next year, and it seems like all would have been better served if Madigan either became the regular 12 or got more time at 10 with Reid getting more time at 12.
MOC brought in Ben Te'o from the Rabbitohs to take over Brian O'Driscoll's 13 spot, which was risky. Te'o hadn't played rugby since he was a kid, and had to re-learn a lot about rugby. And then he broke his arm in the first 20 minutes of his first game. By the end of the season he came good, but for the most part MOC used him as a crash ball runner. MOC also brought Kane Douglas north to play lock, but Douglas had an so-so season, and it ended early with him needing surgery on his back.
And that seemed to sum up much of the season -- lots and lots of injuries, including to noted Irish internationals like Cian Healy and Sean O'Brien, which led to MOC having to constantly shuffle his line up. But the problem was he seemed too conservative and too willing to keep trying combinations that didn't yield much but were safe. What made things worse was that he started to complain a lot in the media, about how he couldn't bring in enough foreign players and how the national set-up forced him to rest players when he needed them. That complaint got louder and louder, until finally it was brought up to Joe Schmidt, who simply said it didn't seem to be a problem for the other provincial coaches -- even Pat Lam, who has far fewer resources at Connacht than O'Connor has at Leinster.
The tries dried up, the defense also flagged, the complaints by and about MOC started to increase about mid-season, and Leinster ended up seeming rudderless and having their worst season in about a decade. It's hard to say it was all MOC's fault; retiring flanker Shane Jennings recently made some pointed comments about how the squad needs to re-learn what it took for them to win league and European hardware five years in a row. But it seemed pretty clear MOC wasn't the man to teach them those lessons.
Let's just say he's not leaving on the best of terms and a year early. It seems he may even have brought up his early release to Leinster himself, and was already looking to go back to Australia. Both parties were happy enough to part ways.