Ok, after taking a few minutes to look a little more in depth, it appears to make sense. I'll summarize for anyone needing this info as well.
Take a basic entry: low_weapons1
low_weapons1 is the group id in the group column, and presumably determines a chance of being chosen among other entries of that group during any operation that would generate loot of that group type. What operations those include isn't clear, in this file at least.
The frequency in the frequency column determines how often an entry of that group is chosen to spawn as opposed to the other entries, again, for that group.
nothing under the commodity id in the commodity column, is the highest percentage to spawn on most groups. I am assuming this is simply no loot at all for that group. Then in place of the other ids that are more specific or need special parameters, you have filters instead of simple ids to determine what other types of things could be included in that group.
Examples:
1) beta_core -- a Beta Core... ok simple enough, this is just a commodity id.
2) ftr_:{tags:[!remnant]} -- this is a little more complicated. It is looking for fighter wings (not fighter blueprints to be clear) by the abbreviation, but specifically (in the variable wrapped by the "}") any ones with tags that are NOT remnant (determined by the "!") in front of tag id). So, in conclusion, all fighters that aren't remnant fighters. Replacing remnant with low would eliminate lowtech fighters, high eliminate hightech fighters, and so on.
3) item_fighter_bp:{tags:[rare_bp, !no_drop]} -- under the blueprints group id, now has a set of tags. It filters to anything under rare_bp that also does not include a no_drop tag.
4) item_:{tags:[package_bp, !no_drop]} -- under the package_bp group. This directly relates to my earlier question: this specific entry, alongside: nothing has a 20/100 frequency to drop an entire blueprint package. If I wanted to include a rarer blueprint package spawn, I could simply add a new entry below:
item_:{tags:[rare_package_bp, !no_drop]}, package_bp, 5
rare_package_bp in the tags array links directly to blueprint packages defined under that id in the special_items.csv file under the tags column.
What this does: Now there are separate types of blueprint packages that will spawn far less often than normal blueprint packages, but will unlock higher tier blueprints. (You can define what types of blueprints are included in each package through special_items.csv)