He's stated that he intends to work towards peace, which ties into the choice of Benedict over Pious. Benedict XV tried hard to end WWI. They are also both scholars so that may be why he chose it too.
But yeah Malachy's predictions really do play into this as an olive branch is a symbol of peace, something Benedict XVI has said he'll work for.
If I remember correctly one of the previous Pious' (X I think) said that someone with his name would be the last pope and that he'd flee Rome over the corpses of his priests.
There are three kinds of lies; lies, damned lies, and statistics.
Mark Twain