Survivors saw the bow rise up for a few moments when she broke in two. I believe the water had not flooded the upper decks and this gave the bow some lift when she was cut free from the stern. The heaviest part of the ship were the engines in the middle, and this may have forced the ship to sink down rapidly in the middle when she broke. How high do you think the bow rose up? I doubt it was many feet, but it was certainly enough to bring the boat deck up.
Here are survivor accounts:
"I reached a collapsible boat that was fastened to the deck by two rings. It could not be moved. During that brief time that I worked on cutting one of those ropes, the Titanic gave a lurch downward and we were in the water up to our hips. She rose again slightly, and I succeeded in cutting the second rope which held her stern. Another lurch threw this boat, myself, off and away from the ship into the water."
"Suddenly, her nose on which I was, seemed to suddenly rise from underneath the water and I and a few more that were close by cut the ropes that held the boat to the falls (davits).
Mrs Ida Hippach
"We heard a fearful explosion. I saw the ship split open. At the same time the ship’s bow rose up in the air as the steamer sank towards the center."
"The ship appeared to split, well forward to midship, and bow or buckle upwards."
Lady Duff Gordon
"A dull explosion shook the air. A louder explosion followed and the bows of the great ship shot upwards out of the water."
Also here is a survivor account in Simon Angel's Titanic book 'Everything Was Against Us':
"Further forward, the water had now spilled on to the boat deck itself and passengers and crew found themselves ankle deep in water. Inexplicably, the ship seemed to struggle to maintain buoyancy, as the water level fell, leaving the area dry once more before surging aft with renewed force in a huge wave."