I don't find any reference to Bakelandt operating in "French Flanders". He certainly did operate in West Flanders (het Vrijbos) and in fact he was captured in my grandmother's hometown of Ichtegem
The reference to French Flanders has already been cut in the second edition, but I thought I would take the occasion to look into the matter (slightly) more deeply. At the bottom of this post is a map showing the approximate locations of the crimes for which Baekelandt and his accomplices were executed, according to the printed Dutch translation of the sentence of the criminal tribunal of the Département Lys brought out at the time:
(Not quite a primary source; there is a 1928 edition of the original trial documents, by Ernest Hosten and Egied Strubbe, that I don't have immediate access to: De bende van Bakelandt: hare misdaden en veroordeeling volgens het bewaarde procesbundel.) The crimes they committed included housebreaking, extorting money with menaces, armed robbery, robbery with violence, highway robbery, murder, and attempted murder. All this took place very firmly within the borders of present-day Belgium. They operated from a number of inns and safehouses and (as my correspondent says) a woodland hide-out in the "Vrijbos", all pretty much in the same area as the crimes and slightly to the west (but not so far west as to be over the present-day border with France).
View Baekelandt in a larger map