This comment has multiple (2) @-notifications:
How is this possible, seeing as
- Jeff mentioned this is a no-no;
- Highly-voted requests of this nature have been declined;
the FAQ on how @replies work explicitly mentions this to be a non-possibility:
You can explicitly notify one (1) other commenter, editor, or ♦ moderator who closed a question.
The comment was clearly not edited after the fact to insert a second @-reply (although this is also not possible).
Here is a more recent comment that has multiple @-notifications:
The use of "possible" in this post is used loosely, as it is clearly possible. I just don't know how.