OR the camper monkey just cut the new hose too short, slid it over the small end of the fitting, realized it was too small, filled it with plumbers putty? and/or forgot to tighten the clamp!
Probably so he didn't have to tell the shop foreman he just cut $30 worth of hose 3" too short........
Hope the OP got er fixed by now. Seems like a straightforward repair.
And yes, if hose clamps backed themselves off with any sort of regularity there would be cars scattered all over the shoulders every day with no coolant in them.
Unless it's a high frequency vibration connection worm gear hose clamps stay as tight as you make them unless you overtighten and strip the clamp.
These hose clamps will loosen occasionally on my snowmachine exhaust. Heat shields, vibration dampers and hot dog coolers get clamped onto the pipe. They loosen up sometimes.
In this instance, a little rtv/silicone gasket sealant works wonders. Like a shock absorber. Fill the screw area and around the screw head with rtv. Dampens the vibrations and kind of acts like thread locker.
Same for exhaust springs.