\begin{align} e &= 2.7182\ldots \\ \varphi &= 1.618 \ldots \\ \pi &= 3.1415\ldots \\ \end{align}
\begin{align}
e^2 &= 7.38905\dots \\
\varphi^2 &= 2.61803\ldots \\
\implies e^2 + \varphi^2 &= 10.00708 \ldots \\
&> \pi^2 \\
&= 9.8696 \ldots
\end{align}
$10.00708 - 9.8696 = 0.137485 \Rightarrow 0.1375 \Rightarrow 137.5$deg is the Golden Angle
How come $\pi$ is short by the value of the Golden Angle?
It is not a right triangle in your diagram above precisely because $\pi^2 \neq \varphi^2 + e^2$.
There is the Kepler triangle, which has sides $(1, \varphi, \sqrt{\varphi})$ for which $$1+\varphi = \varphi^2$$