Stalin referred to the Soviet Union as a republic. Why was this misleading?

The official definition of a republic is any state that doesn't have a monarch. That said, republicanism and republics have been closely affiliated with democracy, because the reason most people hated monarchs in the first place, was because they were not elected by the population.

So while Stalin was right on paper, it is quite misleading because it might lead to some people believing Stalinist Soviet Union was democratic, when in fact it was a dictatorship.