Probably just a failure of the hose. When a hose cracks, it can easily go from no leaks to pissing out coolant. Put a new hose and clamps on it. If you want to be thorough, replace both the radiator hoses and the heater hoses and get a new radiator cap while you're at it.

You can get a coolant pressure test kit as a loaner tool at any of the major parts retailers and put pressure on the system and see if there are any further leaks or if something unexpected is leaking. It's definitely worth doing.

 

Grab some channel locks to squeeze the two tabs on that spring clamp together for removal. Once the hose is off, look for any scale, dirt, or even rubber before shoving the new hose on as it can keep the hose from sealing properly all the way around. If using worm clamps, dont overclamp it. Just enough to squeeze the hose, not dig into it. Some reuse those spring clamps, some dont. If it were mine it would be new hose, new clamp. Which clamp you use is up to you. Aftermarket hoses are sometimes longer than what comes off. Trim it if need be, a little at a time, until youre happy with the fit.

Stick a bucket under the hose and drain it into the bucket. Dont bother with the radiator drain.