Exactly, no harm was intended or done. Somebody posting on your wall doesn't even really impinge on your privacy (Hell, for all intents and purposes Facebook do it for profit). Whatever reward, perhaps reasonably reduced, they pay this guy will be cheaper than any bitterness earned from sitting behind a wall of pedantry with big fat righteous grins on their faces.

If they bothered to look at his profile (it's public), they'd see he looks to be a great fan and tinkerer on the Facebook platform.