Just a minor point, the profession is called naval architects and not marine
You can't tell if a vessel is top heavy just by their looks. If you have ever seen a lightly loaded container ship from the bow or stern, you would wonder how it ever stays upright.
Stability is related to the vessels center of gravity, yes, but it's mostly determined by where the center of buoyancy shifts with respect to the center of gravity....you cannot see this visually. This movement of the center of buoyancy determines the vessels righting moment. The angle at which the righting moment goes negative is the point at which the vessel capsizes.
In this case the naval architect screwed up OR the naval architect was not given the correct data with which to make his calculations. Stability and Trim really is an exact science and not guesswork.
Sailboats typically have a lot more righting moment than a powered boat of the same dimensions because righting moment puts a horizontal load on the sail which creates a greater pressure differential on the weather
and leeward sides of the sail.
An inclining test is used to prove (or possibly disprove) the naval architects stability curves.
The Coast Guard does not do inclining tests, they witness them. Inclining tests are typically only required for vessels that carry passengers for hire which includes Subchapter T and larger commercial
vessels. I have never heard of them witnessing an inclining test for a pleasure boat....but then perhaps this vessel was intended to carry passengers for hire?