No apology needed ... I'm glad you took the time to look.
Pope Leo XIII, for his good points, was in fact a bit of a liberal, and he did make some mistakes that green-lighted the early Modernists that St. Pius X had to deal very forcefully with, especially in the Encyclical Providentissimus Deus. Now, the Encyclical itself is quite sound ... but unfortunately he phrased a few of the more theologically nuanced sections in such a way that the Modernists could easily twist them and convince people that the passages mean what they wanted them to mean. Pius IX had to deal with the same thing, where during his own lifetime word got back to him about how some liberals were interpreting his Encyclicals, and he was incensed by it. St. Pius X, in approving of Newman, was basing his little not entirely on an apologetic work by a bishop who was friendly to Newman.
I've read that there was a huge amount of pressure on the Vatican to embrace Newman because there was some thought that they would be instrumental in kicking off a great wave of conversions from Anglicanism and restore the Church in England.