There is a requirement to give assent to the teachings of the Pope, even when he is not speaking ex cathedra.
"This religious submission of mind and will must be shown in a special way to the authentic magisterium of the Roman Pontiff, even when he is not speaking ex cathedra;
that is, it must be shown in such a way that his supreme magisterium is acknowledged with reverence, the judgments made by him are sincerely adhered to, according to his manifest mind and will.”
~Dogmatic Constitution on the Church #25
Now Lumen Gentium, the Dogmatic Constitution on the Church, is one of the principal documents of the Second Vatican Council. The Constitution was promulgated by Pope Paul VI on November 21, 1964, following approval by the assembled bishops by a vote of 2,151 to 5.
Whether one posits infallibility in Ecumenical Councils or Popes or both, this document is ungainsayable on all counts, and the Pope was most certainly exercising his magisterial authority. In other words, Catholics must give assent of mind and will to all papal teachings.