Wrong.
191. As regards music, let the clear and guiding norms of the Apostolic See be scrupulously observed. Gregorian chant, which the Roman Church considers her own as handed down from antiquity and kept under her close tutelage, is proposed to the faithful as belonging to them also. In certain parts of the liturgy the Church definitely prescribes it;[171] it makes the celebration of the sacred mysteries not only more dignified and solemn but helps very much to increase the faith and devotion of the congregation. For this reason, Our predecessors of immortal memory, Pius X and Pius XI, decree - and We are happy to confirm with Our authority the norms laid down by them - that in seminaries and religious institutes, Gregorian chant be diligently and zealously promoted, and moreover that the old Scholae Cantorum be restored, at least in the principal churches. This has already been done with happy results in not a few places.[172]192. Besides, "so that the faithful take a more active part in divine worship, let Gregorian chant be restored to popular use in the parts proper to the people. Indeed it is very necessary that the faithful attend the sacred ceremonies not as if they were outsiders or mute onlookers, but let them fully appreciate the beauty of the liturgy and take part in the sacred ceremonies, alternating their voices with the priest and the choir, according to the prescribed norms. If, please God, this is done, it will not happen that the congregation hardly ever or only in a low murmur answer the prayers in Latin or in the vernacular."[173] A congregation that is devoutly present at the sacrifice, in which our Savior together with His children redeemed with His sacred blood sings the nuptial hymn of His immense love, cannot keep silent, for "song befits the lover"[174] and, as the ancient saying has it, "he who sings well prays twice." Thus the Church militant, faithful as well as clergy, joins in the hymns of the Church triumphant and with the choirs of angels, and, all together, sing a wondrous and eternal hymn of praise to the most Holy Trinity in keeping with words of the preface, "with whom our voices, too, thou wouldst bid to be admitted."[175]
193. It cannot be said that modem music and singing should be entirely excluded from Catholic worship. For, if they are not profane nor unbecoming to the sacredness of the place and function, and do not spring from a desire of achieving extraordinary and unusual effects, then our churches must admit them since they can contribute in no small way to the splendor of the sacred ceremonies, can lift the mind to higher things and foster true devotion of soul.
194. We also exhort you, Venerable Brethren, to promote with care congregational singing, and to see to its accurate execution with all due dignity, since it easily stirs up and arouses the faith and piety of large gatherings of the faithful. Let the full harmonious singing of our people rise to heaven like the bursting of a thunderous sea[176] and let them testify by the melody of their song to the unity of their hearts and minds[177], as becomes brothers and the children of the same Father. (Pius XII, Mediator Dei)
Wrong.....nope: Right!
You have quoted from an encyclical of Pius XII, where he is suggesting that congregational singing would be a good thing. This is not a legislative document on the mass. Such singing was not required - and certainly not by what Pius said in your quote.
In terms of time, Pius was the last of the old popes - the one of the Tridentine mass. So regardless of what resulted on diocesan or parish levels from his writing (which in fact was very little), it was anything but a long established, and widely followed tradition. There were however local variations in the use and extent of music in low masses. From place to place.
So, I will repeat my statement, as it is correct in light of mystical spirituality, and of the writing and reflections of many saints, beati and scholars:
"The mass is better without music, as then one must concentrate wholly and completely upon the mystical sacrifice and all too real miracle taking place in front of you, under the appearance of bread and wine."
The person who wrote those words - myself - is one who has had much study and training in the field of Sacred Music. So I think I know whereof I speak.