Sin wave spectrum shows multiple frequency
An FFT only results in a single component (plus its complex conjugate and some tiny numerical noise) if the single pure real sinusoid input is of a frequency whose period is an exact integer submultiple of the FFT size.  A rectangular window makes any "leakage" into other non-adjacent bins even worse.

But the length of the FFT you have specified is 512, which is not an exact multiple of the period of your signal (which is 44100/440 = 100.227273).