That’s why I questioned it. I doubt that he said that, especially in the Summa.
“The reason for the predestination of some and reprobation of others (praedestinationis aliquorum, et reprobationis aliorum) must be sought for in the divine goodness.... God wills to manifest his goodness in those whom he predestines, by means of the mercy with which he spares them; and in respect of others whom he reprobates, by means of the justice with which he punishes them. This is the reason why God chooses some (quosdam eligit) and reprobates others (quosdam reprobat).... Yet why he chooses some for glory and reprobates others has no reason except the divine will (non habet rationem nisi divinam voluntatem).”