I know it may be perhaps not same device but I have Dcolor Gd1 just not gigablue branded and I had no such problems with needing a password in fact to be honest i went back into about and it said developer options had already been enabled, i had forgotten but i should have known first thing i do with android if needing to sideload apps.
Also I cannot believe since february no one has enabled developer options or has there been perhaps firmware update , but just looking back at the video i have exact build number and date so perhaps a gigablue thing