Some targeted Facebook posts appear as Public on Page Timeline

When targeting a post through Social, gender and age targets only affect who sees the post in the News Feed. Gender and age targets do not affect visibility on the Facebook Page Timeline. For example, a post targeted to males appears on the Facebook Page as "Public." However, people who liked the page only see the post in their News Feed if they specified they are male on their Facebook user profile.

In contrast, language and geo (location) targets affect the targeting of the post on the Facebook Page to make it appear on the Page Timeline as not "Public." For example, if you target a post to English speakers only, the post is not denoted as "Public" on the Page Timeline. Instead, it only appears on the Page Timeline if when someone with English as a language specified in their Facebook user profile views it. 

See the Facebook Help article https://www.facebook.com/help/352402648173466 for details.