I ran the google you suggested but all I got was the Oliver from Bletso. Also, the Dsrk Lsnthorn refers to him not to the Oliver of Lidiard Tregoze. I see no possibility that the Bletso bunch are ancestors of Matthias unless it was an illegitimate liaison or they were servants who to their gentries name..
Yes I have seen Churchyard's report and I am satisfied that it is accurate but I am hoping for further information.
Back to Fuentarrabia, I think it was a major port for trade with the Arabs. I don't know why it would be since it is on the border of Spain and Francs. Also intriguing is that we have an exact date(4/10/1497) for Oliver's death and his son died in the same place 15 years later.
I think the Huguenots went to England in the late 1600's much too late for Matthias.