It may sound really mean to say something like this but I suspect there was some type of error made during the testing. That would be one way to explain going from ten to zero on voltage. Otherwise, if you are putting a dead short on a battery to drop the voltage that much, you will get lots of bad reactions like smoke or welding. Have you worked on batteries and happened to tap a wrench over onto some part of the frame while getting a positive battery cable off? When I do it, it normally leaves a big black spot on the wrench and sometimes burns my fingers, so I now work really hard to avoid doing that!
But there are times when I am working and get really weird readings that should not happen and if I check carefully something has gone wrong on my test, like a meter lead has slipped out of the meter or I'm on the wrong scale or sometimes, it's just a mental thing and I just plain screwed up.
I hate to admit it but it happens to most of us! I blame it on gremlins!
2015 Winnebago Vista 31KE on 2014 chassis