The ditching damns on the 300 & 400 are very different.
300 is inflatable and operates automatically when you open the underwing exits which in turn pulls the chord linked to the damn.
The 400 ditching damn is/are plastic pieces which need pulling into place in the event of a ditching! Not automatic!!
'smoke' caption relates to smoke being srnsed in either the forward or rear hold. A quick look on the 'check fire detect' panel will show which hold!
Did they fire the extinguisher on this occasion?
Cheers
Lots of tuna
x