Default ordering of git log output

Is it intended behavior that the default git log output (without ordering parameters) can show parents before children? 

The man says:
    Commit Ordering
       By default, the commits are shown in reverse chronological order.
so it tells nothing about parent-to-child relationship.

I‘ve just faced an example in an open source repository, where I reproduced this behavior: a parent is shown before its child. (so if this behavior is not intended I can give the project URL for debugging)

So could you please clarify:
1. Is it true that the rule "no parents before all of its children are shown” is not guaranteed for default ordering?

2. What does "reverse chronological order” mean? How commits are actually sorted in git log? 

// I was always under impression that git log lists commit in the order in which they are “recorded" to the repository (e.g. pulled), since this seems to be both the fastest way, and also pretty acceptable from the ordering point of view.  

Thanks a lot!
-- Kirill.