Knowledge is always good, but St. Thomas Aquinas said curiosity—or the fickle pursuit of unnecessary knowledge—can be a vice. What he meant, and what Fr. Mike means here, is that the methods by which we feed our curiosity, and our motivation for feeding it, can lead to vice if we just want to know something instead of pursuing what we need to know.
Those things we say we have to know about because everyone else is talking about them—like that popular show we say we simply cannot miss, or that things someone did that’s none of our business but we just need to know about it—these things can lead us away from a wholehearted pursuit of truth.
The counterpart virtue of unhealthy curiosity is studiousness, where the motivation and method of pursuing knowledge are correct. Curiosity is a good place to start, but it should always lead to studiousness, the virtue of great minds.