WolframAlpha (online) produces closed form solution to simple NonLinear ODE

Questions
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1

I’m surprised to see WolframAlpha produce a closed solution to nonlinear ODE:

y'' + sin(y) = 0;
%theta(t) `=` 4 tan^{-1}(e^t)

Could someone verify?
When I plot this solution, its not oscillatory at all.
Thank you!