having just started to play with the style editor, I was surprised to find that the user has to check a box (or two) to define a style as swing or even. It's not generated by BIAB based on the style patterns

Get it wrong, and although the style is truly swing, the picker will call it even. So if BIAB did have an indicator based on the style it could easily be incorrect.

BIAB will happily play a song entered as swing with an even style, and vice-versa. You can't even trust Piano roll fully. You really have to look at where the note is entered relative to the start of the beat.

And then of course there are songs that switch styles, or styles that have a genre of jazz but with an even feel.

Obviously it's not an exact science

BIAB for Windows Version 2019 (643)
Windows 10 (1909)