That's not true. Charitable organizations are just one of many groups that qualify as a 501c3.

Groups dedicated to scientific, literary or educational purposes also quality.

The reason this is a problem is that Rebble is using their being a "non-profit" as a point of advertisement but there is essentially no difference between someone owning a for-profit company, and someone controlling and heading a non-profit company where they set their own salary and are not a 501c3.