Note that previous reports had associated that record with the 2003 Seattle team; the Cardinals have subsequently updated their note. It was definitely the 1998 team. I covered that Seahawks team and remember it struggling to an 8-8 finish in Dennis Erickson's final season as head coach.
The chart shows the teams with at least 11 return touchdowns. I've added a column for season records. Arizona and Seattle are the only teams on the list that failed to finish with a winning record despite all those unconventional points.