As above: "The ICT course content of the qualification must be at a professional ICT level with the predominant objective of the course being to educate students to be professionals in ICT."
Additionally (this is all in the ACS Guidelines):
"The objective of the course needs to be appropriate within a broad definition of ICT - a profession trusted by society for conceiving, designing, implementing, maintaining, managing and disposing of ICT infrastructure, products, processes and services within broad professional context. It is expected that a significant objective is to educate students to be ICT professionals."
"A standard 3-year Bachelor level qualification is deemed as having a major in computing if at least 33% of the qualification is ICT. Qualifications that are longer in duration are assessed to the equivalent of a 3- year AQF Level 7 (Bachelor) award."
"A Bachelor or higher qualification is assessed as a Minor when the ICT content is at least two thirds of the requirements for a major."
"All qualifications with ICT content less than the requirement for a Minor are assessed as Non-ICT qualifications."
Web Designer is not assessed by ACS but by VETASSESS; it is not the same as Web Developer, which is assessed by ACS. I assume that ACS considered there was insufficient ICT content, by their definition, in your course for it to be considered to have either a major or minor ICT content when assessed against the above criteria.