I did not claim that it is always true, if by “always” you mean the genetic manipulation of any nucleotide sequence in any organism with any technology that we can reasonably foresee in the next 50 years.
But this virus did not arise through genetic manipulation. This was immediately clear, see for example this Nature paper from March last year.
For background, it is an extremely difficult problem to predict protein structure (and hence protein function) from amino acid sequence. As it happens, there was a major breakthrough just a few months ago.
To return to the first paper, with the background that current protein structure-function technology is limited to predicting the effects of modifications to known structures:
In SARS-Cov-2 the structure of the Receptor Binding Domain of the spike protein is not a predictable higher-affinity derivative of other coronaviruses, so the mutations are not plausible candidates that would have been introduced if humans had deliberately manipulated an existing virus. It is a novel structural solution that could only plausibly have been found by natural selection.
There are several other supporting technical lines of evidence described in the paper, all of which support the origin of the virus through many generations of mutation and natural selection in the wild.