The course notes state that in ANOVA

The course notes state that in ANOVA A factor is an explanatory variable that exists at different levels, the levels being controlled by the experimenter. Levels of factors may be either qualitative or quantitative, and the set of factors levels applied to a particular experimental unit may be thought of as treatments in the context of the experiment. However in the review summary for ANOVA ANOVA model can be viewed as a special linear regression model where all the predictors are categorical variables (factors) Can you kindly help me understand this better.  Aren't categorical quantitative