That depends on why he was cleared. If he was cleared due to some sort of technicality or due to lack of evidence then there is no reason why he cannot be prosecuted a second time. Also if any of the relevant laws have changed in any way since 2007 (which I imagine they have) then the prosecutors can try again under these new laws. Being cleared doesn't in and of itself mean that what you where accused of isn't illegal.

wouldn't each new torrent uploaded be a separate case of copyright infringement that could be tried?

The torrents themselves are not copyright. They contain no copyrighted data. He didn't actually share the copyrighted data, just provided a facility for others to share the torrents.

i'm aware of that, but that doesn't mean someone won't still try to drag him to court for them.