The discovery of an unpublished commentary on the Targum of Onkelos induced him to study Aramaic (preface to his "Oheb Ger").
Unfortunately, it was then mistitled as a manuscript of Targum Onkelos until 1949, when Alejandro Díez Macho noticed that it differed significantly from Targum Onkelos.
At that time Targum Neofiti was titled incorrectly as a manuscript of Targum Onkelos, and it remained unremarked until 1949, when Professor Jose Maria Millas Vallicrosa and Alejandro Díez Macho noticed that it differed significantly from Targum Onkelos.