The actual reason for the lengthy delay was a ground stop due to enroute weather.

However, there is a system limitation which causes only the text for the first delay code entered to be displayed on nwa.com (actual flight times and delay codes are entered in a system called WorldFlight, which then sends the data to PARS). As a result, any additional delay reasons entered in WorldFlight are not always displayed in PARS or NWA.com because there is only room for one code there.

In this case, I'm guessing there may have initially been a minor delay in boarding due to passenger accommodation (e.g. unaccompanied minors, wheelchairs, elderly, etc.) but once the weather delay occurred the update to the reason code never made it to PARS; therefore it didn't display on NWA.com.