It's fine to praise Russian culture, which is indeed great. It's not fine to praise the Russian Empire, especially now. And it's ridiculous he spoke to a Russian audience without clearly condemning the war.
This will rank alongside Francis' previous remarks to the effect that "the cruellest [Russian forces] are perhaps those who are of Russia but are not of the Russian tradition, such as the Chechens, the Buryati and so on." It's certainly true Russian troops who are not ethnic Russians have committed atrocities. But by far the greatest cruelties of the Russian invasion are the mass killings and deportations ordered by Vladimir Putin and other top-level officials - the vast majority of whom are in fact "of the Russian tradition."
Francis would do well to study how his predecessor, John Paul II, spoke about the Soviet empire and other communist states (including his home country of Poland). He might learn something useful.