It is given that there are three samples involve in the ANOVA. Therefore,
The ANOVA is a technique which is used to determine whether the population of more than two groups are significantly different or not.
Here, there are 3 sample groups available in the ANOVA, it means that the population means would be 3 as well.
Thus, for the given case, we are trying to determine whether these three population groups' means are significantly different or not.