First question: is this how they were set up, to turn over with key off.
Second question: Does starter draw that much to flatten battery that quick, or did starter overheat.
Yes, they were set up that way, you need to remember to turn the key on... "duh"
Back then the vast majority of all cars, trucks, and equipment had separate from the ignition switch; a starter button, switch, or linkage.
Probably wasn't as much of a problem then because that's the way they all were.
Now with drivers that are accustomed to combined ignition and start switches it's more of a problem if you can call it that.
Yes, starter draws that much, and you may have also over heated it, or at least got it warm.
It's a general rule of thumb to crank no longer than 5 or 10 seconds at a time and then wait for preferably a few minutes between attempts.
Accomplishes two things, lets the starter cool, and gives the operator time to think about what's going on, why it won't start, and what can be done about it (like turn the ignition on)

Grigg