Assuming you can normally store with batteries disconnected for the same length of time (some find there is still a load even when disconnected) - it sounds like the batteries were left in - or accidentally switched to - use...
As fulltimer50 said - there is no electrical connection there - even with batteries in 'use'...
If you hadn't stored it as long in past - you might have a small load still on the coach batteries when in 'store' that caused them to drain.
Not yet retired...
Florida (Michigan transplant)
2014 Hurricane 32A
2000 Infinity (previous)