Probably even more have been burned by overdesign.

If you decided to make your boolean a timestamp, and now realize you need a field with 3 states, now what?

If you'd kept your boolean, you could convert the field from BOOL to TINYINT without changing any data. [0, 1] becomes [0, 1, 2] easily.

While I agree on the over-design point, it doesn't follow that the BOOL is trivially convertible to a TINYINT. In some databases a BOOL is stored as a single bit.