Indeed, looking even a bit deeper into this I found where the story appear to have originated, in "
The Life, Times, And Missionary Enterprises, Of The Rev. John Campbell" where it is attributed to a a scottish judge from the XVIIIth century, named David Dalrymple (who bore the title of Lord Hailes).
The problem with that is obvious, it is an unsupported anecdote. We have no way of confirming that Dalrymple's findings were correct or that, even, he did truly say that. The "Life and Time", after all, was not published until almost 50 years after the death of Lord Hailes and, from what I read, immediately arose suspicions.
The whole affair is detailled in quite a lot of detail
here but, in my opinion, what we have is an unsupported annecdote (I suspect, an example of a pious lie) that has been cheerfully and uncritically discovered by some apologetist and has then been uncritically copied in the apologetist community (in, to use Rincewind bon-mot, quite an incestuous manner) without any serious regard as to its correctness.
As far as I am concerned, it is an urban legend propagated by confirmation seeking believers...
Now, I have been wrong before (once, in 1982) but I'd need to be pointed out at some actual scholarly work rather than a second-hand quote about a doubtful anecdote...