Leak caused overheating??

It's hard to say without knowing more details, such as, were you low on water?

You "may" have a clogged radiator, or possibly your radiator is just working nicely. The top hose is the water coming out of the block. If that hose is hot, it is telling you the thermostat is open and hot water is flowing through it, into the radiator.

The lower hose is the suction side. As water flows downward through the radiator, it cools. The cooler water gets sucked up into the block to cool it back down. Your lower hose "may" have been coller because your radiator was doing its job, or.... it is possible that you have a clog and the hot water towards the top is not flowing through the radiator to allow it to cool, thus not really heating the lower hose. I kind of doubt that though. Radiators don't just clog suddenly.

You may have just had a pin hole in the hose and it "peed" out water over a little bit of time. Your system only holds about 2 and a half gallons of water, so lose 1 gallon and you're at half capacity, thus making it hard to keep that engine cool.

Your cooling system "pressurizes" when you drive the car. A pin hole will pee out water faster when the car is at temperature because the system has pressurized.

How has you car changed to where a factory pre-bent hose won't work? Are you running a non-1969 or 1970 radiator? A non 1969 or 1970 water pump? Hoses today are made as "cut-to-fit" so the hose manufacturers can make one hose to fit several vehicles and you have to cut off what makes the hose too long for your car. Gates hoses (and belts) are my choice in hoses (and belts) too.

What I do is I buy the factory bent hose at Napa, then I go to Discount or AutoZone and look at their flex hoses and see which has the removable spring in it. They are now making some flex hoses without removable springs that are built into the rubber of the hose. Those can't be removed. I remove the spring out of the flex hose I buy, install it in the pre-bent lower hose, and then put the hose on the car.

On another note, I also test ALL thermostats before I install them. A high-range meat thermometer goes above 210 degrees or so. I start a pot of water boiling on the stove with the thermostat in it. When the temperature rises on the meat thermometer I watch to see if the thermostat opens at about the correct operating range. If it opens I remove it from the pot and let it cool. Then I install it in the car. NEVER run a motor without a thermostat in it.

IF you ever come out of a store, house, etc and see a large puddle or leak, coming from your car, under your car, you can drive a car with a minor cooling system leak if you drive it slowly with the radiator cap at the first released position on the radiator so the system doesn't pressurize. Your cooling capabilities will be lowered a bit but driving slowly offsets this issue. If you are driving a long way carefully checking the water along the way is necessary too. I have done this several times without any problems.

Air pockets will work their way out of a motor as the water circulates. A pin hole leak, in the lower hose, can cause the water to drain but it will drain out of the radiator and the motor at the same time.

At least you found the leak. Losing pressure in the cooling system will cause overheating as in my case on another car where we couldn't see any leaks but it did overheat. The leak finally showed up in the solder joints of the radiator tank.