Yup, there are many things that do not add up here. Yes, the sprinklers should have gone off as well as the fire alarm.
Look at the damage to the exterior of the ship. That metal melted, That is some pretty high temps even if the structure was aluminum.
Melting Point: 660.37 °C (933.52 K, 1220.666 °F)
That's pretty hot folks.
And if it were partial/total steel .... Most steel has other metals added to tune its properties, like strength, corrosion resistance, or ease of fabrication. Steel is just the element iron that has been processed to control the amount of carbon. Iron, out of the ground, melts at around 1510 degrees C (2750°F). Steel often melts at around 1370 degrees C (2500°F).
SS Norway (12 times) '85 - '97; Radiance OS 06/01; Island Princess 11/04, Grand Princess 11/04/05, Golden Princess 7/21/06, Golden Princess 2/24/07, Explorer of the Seas 12/23/07, Island Princess 11/15/08