Yes, the account in question has been deleted. (In general, accounts which are greyed out either belong to a now-deleted account, or, in the case of migrated questions, possibly to an account that was never created. When an account is deleted, the display name is reverted to the default
Voluntary account deletions can happen in basically two ways:
- Users with very low activity can delete their own accounts from their profiles.
- Requests for account deletion can be made via the contact us link at the bottom of every page.
Of course, from time-to-time moderators discover accounts that have been created with nefarious motives (frequently sock-puppetry or suspension circumvention). When such accounts are discovered, they are usually unceremoniously deleted by the mods. Accounts created with the purpose of posting spam and other nonsense are simply destroyed by moderators when found, which has further implications.