I´m with you it looks a little bit strange and confusing but “priority” in this case means, in which order the packages will be loaded, comparing like in the previous version with the line.
“Translated” means the new system:
Prio 1 = lowest priority - this package will be loaded first
Prio x = highest priority - this package will be loaded as last and “overwrite/overrule” possible packages which are loaded before
Hope that helps and makes something “clearer” - this new system is WIP and I´m pretty sure, that ASOBO will improve this feature (which is a good and better one in my eyes) in the near future.