I am very sure because it's written on the site where they describe how CRS is calculated for Education Skill Transferability -
Two or more *post-secondary* program credentials AND at least one of these credentials was issued on completion of a post-secondary program of three years or longer.
System gives out ITA based on what you indicate in profile. For this diploma, you will need to select level of education as secondary ( if I recall correctly, the system asks you to input only post-secondary education, which in this case, is a 3 years bachelors). So you either need to leave it out of your profile or indicate it as a secondary education.