Funny thing is, I contacted the ex-buyer several times over the last 12 months to try to buy the domain, but they told me they had 'other plans for it'.
Very odd.
As you say very odd, I'd love to see a post one day from an ex-owner explaining how this type of thing happens. In my mind it plays out in one of these ways.
1) The one who first signed up for the domain with his own work email address gets retrenched/fired or resigns and all the renewal emails get sent into the inter-ether and disappear.
2) The company or division gets sold to a new owner and in the transferal of assets the domain licenses are forgotten about. Often a precursor to this is the SSL certificates expiring.
3) The IT division decides to update DNS settings and forgets to add the MX record for another domain which happens to control the renewal emails for all the other domain licenses owned by the company.
4) An ex-owner thinks (rightly or wrongly) that a domain has been renewed BUT the registrar has not actually renewed it and it gets purged.
5) The ex-owner deliberately let it lapse and we stumbled upon their trash and realised it was gold
6) The owner is so busy negotiating a sale that they forget to renew the license.