That's a good point. It could be that Walmart themselves wanted this domain to protect their brand. That does in fact happen often.
The thing is sometimes these big companies will protect themselves by acquiring the domains through UDRP or lawsuit rather than outright buying the domain from someone. They don't want to send the message that they'll pay you or I for a domain that we grabbed because it was 'close' to their name.
Instead they'll send the message with a lawsuit that you better not go after similar protected names. And that action would be my concern with owning that name. Hopefully the buyer has a plan, because if they're not Walmart they could have Walmart coming after them in the future.
RE: Weekly Top 20 Domain Name Sales - Week 38