Rav Galico writes that the verse calls Haman’s advisers wise because these were those of his friends who were wise.
The M’nos HaLevi say they were wise due to the straight talk they provide. Therefore, the verse calls them “wise” instead of “loved ones.”
According to the Talmud (Megillah 16a), anyone who says something wise, whether Jew or gentile, is called wise. After all, the Talmud (Megillah 6b) admits that there is wisdom among the gentile nations.
R’ Shlomo Kluger says they were wise because they saw that all of these events Haman described did not just happen, but occurred due to the snowball effect that have built up over many years – perhaps since the time of Amalek.
R’ Mendel Weinbach says they are wise because all wisdom can come from the Torah. The Vilna Gaon, for instance, could purportedly give entire discourses on calculus without ever having seen a textbook on the subject.
Rav Avraham Chadida writes that these advisers knew that when things are out of their expected order are a sign that something good is about to occur. He gives the example of Rivka’s wonder at her unusual pains in pregnancy (Bireishis 25:22), Moshe’s curiosity at the burning bush (Shemos 3:2-3), and even cold weather in the middle of a summer.
Shar bas Rabim notes that the Talmud (Tamid 32a) defines a wise person as “haro’eh es hanolad,” or someone who can predict future events by logically observing history. Actually, these advisers were indeed correct!