Thats not what she says at allscholar Katherine Forsyth has convincingly demonstrated that the Pictish language was thoroughly Celtic, and not a throwback or a surviving pocket of a pre-Indo-European world.
this is what she says on page 41 of Language in Pictland
Pre celticI do not rule out the possibility of a pre celtic substratum influence on pictish, In fact I regard it as all but certain
what can she mean
how could there be a pre celtic influence on pictish if as you claim the picts were actually misidentified celts

your second quote if you had actually read it actually supports my view
Katherine Forsyth says at the end of Language in Pictland that you should leave it to the linguists to decide"The Irish Attocotti and the Picts were probably Celtic peoples, although some linguists claim to be able to detect a pre-Indo-European element in the Pictish language" p263
B. Cunliffe The Ancient Celts (London. Penguin Books.1999) ISBN 0140254226
and the linguists say that pictish is a pre celtic language
so there
