You are very right.
The radiator cap is suppose to vent at certain pressure (~15psi) that builds up with heat of a running engine.
When the engine cools down, any 'steam' bubbles in the engine cooling chambers contract creating some vacuum that sucks back coolant from the reservoir.
If the hoses are weak, their easy path is flattening under the vacuum instead of pulling coolant from the reservoir.
Now if the hose at the reservoir is clogged, it will happen too.
If the hoses are that much thin and bad, staying collapsed by hours/days, deforms them permanently and loose stiffness to rebound.

If there is debris in the coolant reservoir and the debris is sucked by the pipe and sticks to its end opening, can also prevent the vacuum to pull coolant from the reservoir and causes hoses to collapse.

It happened to me in a similar way with the fuel tank of my RX7 : It was factory painted inside. Paint deteriorated with time and flakes the size of ~1/2" were resting in the bottom. Car always started fine, and after a while, with movement of fuel caused by car moving, cornering... flakes that went into suspension in the fuel were sucked by the pipe and blocked flow (no sock), stopping the engine in the middle of anywhere.
Turning the key off, the fuel pump stopped suctioning and the flakes dove to the tank bottom again. And restarted with no problem, everytime, to ramdomly repeat the cycle minutes later on the freeway.

Was a major nightmare to diagnose, that will never forget in my life.