The composer's name is listed as “I.P.S.” in the piece titles and as “Ioannes Patersi Schweling” in the table of contents.
The composer's name is indeed “Sweelinck,” but the fantasia listed here is not included in modern complete editions, so the possibility of it being a forgery remains. However, I lack the expertise to determine this, so for now, I will rely on the information from the manuscript.
Hans Leo Hassler(1564-1612)
70. Ricercar Noni toni. Joh. Leo Has:
The third volume of the Torino manuscript contains a Ricercar in the same mode, but it is a different piece. The piece introduced today has more of a toccata character than a Ricercar.