Obviously beating Tyson meant a lot to him. That fight flew in air for the long time.
I think in Lennox's head it's his biggest win regardless Tyson was a mess.
After that Lennox wasn't really that much into it - not necessarily physically (I think if prepared he could fight for few more years). Having tough night with hungry Vitali helped him make his mind. Nothing wrong with it - he chose right time to retire.