- The laws on official secrets typically (and uncontroversially IMO) forbid any unauthorized handling or distribution of classified material. This is not a US-pandering post-9-11 knee-jerk thing, it goes back at least to WWII, and probably much longer.
- Many facts are classified, even though they don't appear significant. Sometimes they indeed aren't, sometimes the motivation is that a multitude of such facts collectively suggest something which is significant.
- Telling an uncleared person what is classified amounts to giving that person even more classified material that they're not allowed to have. Obviously, so is saying that there's classified material on the page at all, but arguably less so.
- There are some items on the Wikipedia page in question that have "citation needed", ie. they are not immediately obviously sourced from publicly accessible material. Chances are that the problematic material is among those facts.