Nope, I don't think it is: github.com/lichess-org/lila/blob/master/modules/forum/src/main/MentionNotifier.scala Searching the code base for "thibault" also doesn't show anything (relevant).
The link from earlier is just the old change in the history when it was added but it has since been removed again (when the general mention setting was added): github.com/lichess-org/lila/commit/b15af9436a5d1f49016248530bb7137cd7c9a498#diff-c72a4657030fc716e11ff1e8d59ac747a7f21aa09c35f25a013271449ad8a700
The link from earlier is just the old change in the history when it was added but it has since been removed again (when the general mention setting was added): github.com/lichess-org/lila/commit/b15af9436a5d1f49016248530bb7137cd7c9a498#diff-c72a4657030fc716e11ff1e8d59ac747a7f21aa09c35f25a013271449ad8a700