It is completely untrue that honours courses require a dissertation. It may be true in some subjects, but that's not where the difference lies.
University degrees are graded as
1st Class Honours - top standard ie like A-star at A-Level, or a 9 at GCSE
2:1 Honours - like an A or high B at A-Level or 7/8 at GCSE
2:2 Honours - Like a low B or C at A-Level or a 6 at GCSE
Third Class Honours - Like a D at A-Level
Ordinary Degree, which is a basic pass, like an E at A-Level or a grade 5 at GCSE. Anything less is a fail.
Like at GCSE where in Maths you can take a Higher paper and score anything from 5 to 9, or you can take a more basic paper and can score 1-5 but cannot access grades 6-9 even if you score 100%, there are some university courses that are equivalent to the basic option, you can pass or fail but you cannot get honours. An ordinary degree from a course without honours content is worth the same as an ordinary degree where the student took the honours exams but didn't score high enough for the honours grade, exactly like how if someone has a grade 5 Maths GCSE it's worth the same whether they got it by getting a top grade on the basic paper or a low grade on the Higher paper.
Including a dissertation module is one option that some universities may use as part of their honours content.