The crux of the case is there was a witness, walking his dog. So he became the 'persons'.
And it was his complaint and then his evidence that caused and then won the case. The fact that he was an ATPL IIRC probably means he knew his air law - whether that had any influence either way I do not know. It probably had some influence on his credibility, I do not know if his motivation was questioned.
I was under the impression that in order for such a claim to be upheld, there need to be at least two, independent witnesses?