Oh, I'm not saying that it was liberal in the modern sense of the word. And yes, most of those subjects' rights that I'm talking about pertained mostly to the nobles and the educated classes -
that was the big difference between Russia and, say, Austria, not so much the difference in the day to day lives of peasants (although wrt the latter, the difference is that things were actually getting
worse in Russia at the time, as serfdom - already some of the harshest in Europe - became more and more like full-fledged chattel slavery; but that problem would peak later, not under Peter).
But the important thing that this did was to establish the concept of the rights of the subjects vis a vis their rulers, and the requirement for the latter to maintain the legitimacy of their rule. When liberal thought emerged much later, it built on those concepts, extending them to larger segments of the population. In Russia, this happened as well eventually, but much slower.