Did I describe the following concept correctly?
That's a great translation.  Other words that may fit like impulsive


hasty
imprudent


@ChrisW mentions in a comment that kusala means skillful, so a +kusala would mean the negation of kusala (if you look at how sanskrit works), thus another word may be unskillful  and it sounds like your meditation friend was trying to expound on what that term actually means.

Many words have nuances that can become lost in translation, so sometimes it is good to leave words untranslated, or look at how they were constructed.  For example: we could not say "pulsive" as the negation of "impulsive" even though "possible" and "impossible" have the same relationship as "kusala" and "akusala" -- it just depends.  Again, good translation, but be open to the idea that not everything need be translated (and thus nuance can be ushered into a new language body and preserved)