People everyday buy mass amount of names depending on what they believe it may be worth in the future.

The term "bit" and "coin" is very common.

It only makes sense someone bought the domain name bitcoins during the internet boom.

Once Bitcoins became what we know today, any domain name that contained "bitcoin" and similar increased value.

The domain was spotted on the waybackmachine back in 2008 it looks like, being parked by GoDaddy which is a common trait for people who buy domains to speculate future events.