An accident of the English language; some people would insist on "chairperson" there, and some older people might still insist on "chairman" but that's becoming less and less acceptable over time. As an even better example, there's "fluke":

1. A fish, and a flatworm.

2. The end parts of an anchor.

3. The fins on a whale's tail.

4. A stroke of luck.

The meanings are etymologically distinct (for the most part) and it's only chance they ended up wit the same spelling and pronunciation.

If that's philosophically troublesome, linguistics is not for you.