I made a call to a friend that is a research chemist for Dow chemical. She has a Masters and P.H.D. in research chemistry.
She said to get an e-glycol vapor explosion (entirely possible) you need a continuous heat source heating an open container of e-glycol in an enclosed area for an extended period of time. Any other scenario, no boom. That is why it is so safe in cars.
She thinks some other chemical blew the garage (like gas).
I'm sure your source can figure out the size of the aerosol droplets that will enable the water to be shed quickly while leaving the e-glocal airborn until 4:30 AM when she starts the engine!
Else I’m thinking the possibility of murder may have crept back into the picture.