Is someone who registered over 4 years ago likely to be a spam bot?
No, nor are they likely to post the above. They could easily have become owned by a spambot that is spamming blogs, forums and whatever that they belong to, or has simply harvested the means of doing so.

A lot of people save their login details because they don't see site memberships as being valuable data.

It is obviously of value to spammers, if you see the efforts that they make to set up accounts of their own. Finding ready made accounts to sites is an item of value just like bank account and credit card details.