Apparently, it can happen if wine gets warm, it can start fermenting causing a build-up of carbon dioxide and the resulting pressure could cause the bottle to explode. Another reason seems to be if a bottle has been damaged, even if not visibly, the glass may be weakened and explode.

I'm sorry you were faced with a horrible mess to clean up.

I would think if it exploded, there would be wine sprayed much farther than if it just fell on the floor. You need a forensic detective, lol! I hope your floor isn't destroyed by wine stains. And I do think, if the wine wasn't fully fermented before bottling, that it could build up gas if it became warm enough and possibly shaken by transporting it. It wasn't homemade wine, was it?

Yikes, here's a youtube video of an exploded bottle:

If it had exploded, there would be wine on the wall or cabinet behind the shelf and on the shelf above as well. If there is only wine on the floor, I would guess that it fell.

Was it cold there? I left a bottle of red wine vinegar in our lake house (unheated) over the winter and the bottom broke. It must have happened early in the winter because it had dried up already. Not too much of a mess to clean up!

Well it must have fallen and hit the floor just right to shatter into a million pieces. All cleaned up but for some permanent stains on the baseboard and a few on the wall which of course could be painted if I cared. Since it’s down by the floor under a shelf I don’t.

I know by experience that they can explode in extreme heat. Red wine bottle in car left outside during 100 degree day--oh my! I had to take it to a specialty car wash to get the stains and smell out.