Hallo,
At least in my reviews, it means:
Are scripts used for that mission ? Do they fit to the mission. Do they have bugs, are they easy to use (if there is some player interaction)?
I do not care who made that script (this info should be in the Readme). So IMHO i am not rating the ability of the author, i am rating the mission. Therefore if someone makes a fantastic mission with AddOns and Scripts made by other people, he will get a high grade, too. (The only possiblity to avoid this high grade is not to give credits to the makers in the readme and i find it out ;D ).
Of course "home"-made scripts normally fit better into a mission, but they are also more likely to contain bugs
Greetings
Kuro
P.S. Just for the extrem cases a mission without scripting, but with works well without it (rare). Normally gets a 4 in scripting. So i have the possiblity to point out bad scripting. IMHO No Scripting is better than buggy scripting.