Yeah sleep-wake problems often are related to things missing or broken in the (poorly constructed) system.

If the software on the car was poorly written, it may not have had a good back-off on the fob check, or if the fob itself was malfunctioning it may have left the car in a weird state.

While I wouldn't expect a fob to drain a car, it certainly doesn't seem implausible, especially given what the fix is.