Difference Fourier Shift Theorem and Cross Correlation Theorem
First of all, what you quote as the Cross correlation Theorem 


  the cross-correlation between two signals is equal to the product of fourier transform of one signal multiplied by complex conjugate of fourier transform of another signal


doesn't make much sense: the product mentioned above gives the _cross_power spectral density function, and not the cross-correlation function at all. The cross-correlation function is the inverse Fourier transform of the cross-power spectral density function, namely, the product mentioned above.

That being said, the key difference between what you are doing and what the Cross-Correlation Theorem is that you are using a special case that is perhaps better termed the Autocorrelation function theorem.  Notice the use of the word another (next to last word in the highlighted wording above). When another is replaced by the same, we get that the autocorrelation function is the inverse Fourier transform of the power spectral density.