I'm thinking he was probably confused since it was a punt not a kickoff
It's funny how NFL.com has it recorded on their official play by play:
4-1-SEA 43 (:51) 9-J.Ryan punts 44 yards to ARI 13, Center-49-C.Gresham. 21-P.Peterson to ARI 8 for -5 yards (31-K.Chancellor). FUMBLES (31-K.Chancellor), recovered by ARI-20-A.Jefferson at ARI 6. 20-A.Jefferson to ARI 23 for 17 yards (35-K.Cox). After the punt was received, the ball was lateraled and fumbled.
So they call it a fumble, then at the end they concede it was a lateral but then still call it a fumble. I guess because the pass wasn't handled cleanly because of Chancellor.