In the Council of Florence, there are two very interesting decrees that one ought to be aware of. They are dogmatic definitions and decrees, which definitively prove that the absolute necessity of receiving the sacrament in water is in fact a dogma that must be believed by divine and Catholic Faith.
But his very words make clear that St. Thomas was not expounding on what he believed to be an article of Faith, but was rather SPECULATING. This is undeniable from the words "it SEEMS that", hence, it was merely his opinion.
In short, he knew of St. Thomas' opinion, but dogmatically shut the door on it forever (in fact, the door was already shut on it at the Council of Vienne in 1311-1312, just a few decades after St. Thomas passed away)
What Must You Do To Get to Heaven?