How to interpret a P0AA6 error code that "went away"?

Last week I drove my car without problem for 1 minute to a local store, shopped, and then when I restarted all dashboard lights came on and I couldn't put my Prius into Drive or Reverse. AAA checked the 12 volt battery and it showed good. Didn't know what else to do, so they towed it to my trusted repair shop. They hooked it up and got a P0AA6 (they had replaced the hybrid battery 18 months ago with a Dorman, said they had had nothing but bad luck with those and it needed another new one).

Thanks to this forum, I learned that I needed to know the subcode too (thank you forum!!). They didn't record what the subcode was, so I asked them to hook it back up to get that and when they did... no problem now! They said they've driven my car 10 miles (I think 5 miles on each of two different days) and can't make the problem recur.

1. What are the most likely explanations for a P0AA6 code going away like this? I get the impression battery corrosion (around the screw) might be one...

2. Depending on your thoughts re: #1, would it be safe to continue driving it in-city? Another post I came across noted that battery cell explosion might be an issue and I got the impression that could be really bad, maybe fatal.

Thanks... really appreciate the advice of the smart folks here!!