The equation above indicated 146 Hz, and the Nielsen equationNielsen, A. K., "Acoustical resonators of circular cross section and with axial symmetry", Transactions of the Danish Academy of Technical Science, 1949. indicated 138 Hz. Clearly, the whistle was being driven by a cavity resonance. This is an example of a whistle being driven in edge-tone fashion, but the result is a monopole sound field.
