There is no "line", because those descriptions have no accepted or agreed upon metrics.
The "hobby jogger" thing is simply a loosely defined term thrown around in here as an ironic epithet of sorts designed to deride any "civilian" who never achieved at a minimum "sub-elite" status.
Don't worry about it. Everybody that runs with a goal at the edge of what their genetic ability
allows is "serious", it doesn't matter what that ends up being.
However, if you must have a "cutoff", the numbers you mentioned seem reasonable. Most others in here would probably skew 1/2 hour lower for each gender, which roughly gets you into BQ territory for both of the "open" categories.