It is a fact, purposely infecting test animals and selecting for the most virulent mutations would be INDISTINGUISHABLE from natural mutation, because it is nothing more than accelerating a natural process and selecting for desirable traits.
From the
abstract cited in your article:
...We genetically modified A/H5N1 virus by site-directed mutagenesis and subsequent serial passage in ferrets. The genetically modified A/H5N1 virus acquired mutations during passage in ferrets, ultimately becoming airborne transmissible in ferrets.
"Site-directed mutagenesis" is NOT a natural process. Convenient how they left that tidbit out.
SDM is an in vitro procedure that uses custom designed oligonucleotide primers to confer a desired mutation in a double-stranded DNA plasmid.
There is no evidence that this has been excluded as a possibility, and any claims otherwise are assumptions, not based on observable empirical data.
You really don't understand concepts of proof and evidence. The burden of proof is on you to
prove that the virus was created in a lab. It's not anybody's job to prove that its not. Just flinging improbabilities out there and then saying they are likely is nothing but you propelling baseless conspiracy theories.