If it were imported slang that could explain it, but still.
How do you feel about 1800's history writing?
The same might be true for etymologies provided in this dictionary.
I'm sceptical until I see the text material this etymology is based on.
Besides the question of etymology, Welsh "ch" is a digraph representing a velar fricative, just like it does in Dutch and German. It makes little sense to link it to our EVA transcription of [ch] in any way.
If you would find the time to look in the Welsh and the dialect you will find many reasons (read: words) that are interesting with respect to the VMS.
One of the most interesting words is CROT or CROL as mentioned here. Basis for that word however is not Welsh perse, but Old English.
I already gave somewhere here on the forum more and specific information where to find it exactly, I believe a year ago.
(There are other considerations why I did not went on with Welsh further, mainly because of time, place and cultural arguments)