Having a medical marijuana card, I believe, counts as illegal drug use. Legal in Hawaii, but illegal at the Federal level so you fail the NICS. From what I understand it remains that way until your card has been expired for a year. That could account for the drug use denial.
Medical marijuana may not be the "cause" in this instance. The 2012 report, on page 10, had some denials listed for medical marijuana as separate entries, and like you say, those are federal NICS nono's. It's not stated in the report how many of the "one or more disqualifying factors" (also called cause) were caught at the NICS level, and how many were denied at the discretion of the police. The other denial cause jumped out at me because it was not specific- simply "admitted illegal drug use".
I'm wondering how much discretion the police have to deny based on their own "rules" verses federal rules. Or if the police even have any rules. Does the chief just get to decide what constitutes denial for their part of the background check? That's why I compared "admitted illegal drug use" cause to the 12 year old bed wetter getting denied. Dr Cooper mentions the bedwetter in the video, and I'm pretty sure that wasn't caught at NICS level (wasn't federal). Dr Cooper didn't say the bedwetting denial took place in 2012, but sometime during his tenure.
Below is a snippet of page 10 table of the report. Full report PDF at:
http://ag.hawaii.gov/cpja/files/2013/03/Firearm-Registrations-2012.pdf It's a good read.
Table 3: Descriptions of Firearm Permit Application Denials,
State of Hawaii, 2012
[N = 227 Denials] # %*
accidental death felony 1 .4
adjudicated mental defective 1 .4
admitted illegal drug use 1 .4assault 29 12.8
drug offense 17 7.5
drug offense + medical marijuana patient 6 2.6
medical clearance needed 7 3.1
medical marijuana patient 4 1.8
mental health treatment 10 4.4
no response from California re status of marijuana arrest 1 .4
substance abuse treatment 3 1.3
If there are no "rules" the police must follow to determine "cause" beyond the NICS level, then this sure gives them lots of discretion. Perhaps not a good thing to have that much power over the process.