Why is this music chosen for a Catholic Mass? At 06:00 in this video (Levithögmässa. 23 november 2019, Göteborg) of Mass in the Extraordinary Form, some special music is performed. Why would anyone choose what I refer to as "concert music" for Mass? Why do some people have this instead of normal church music? I do not hear this as church music at all. Why is this music choosen in stead of normal standard church music? I can see Gregorian Chant and hymns as church music, but this does not sound like "church" at all. Please help me understand this.
This music that you think of as 'concert music' was originally church music.

I don't recognize the specific piece in the video, but pieces of a similar style were originally written to be used in church services. Most classical music with "Mass" or "Requiem" in the title (or linguistic variants such as "Missa" or "Messe") were intended to be used in celebrations of the Mass. This includes works by Haydn, Mozart, Beethoven, Verdi and Bach among many others.

The words being sung are actually the prayers said during mass, and the sung versions are used in place of the recited prayers.

The music is commonly called choral or church music, and has been part of Catholic and other traditions for many centuries. These settings require a high quality choir to do well, so you will usually hear them only in larger churches and cathederals - and with changing musical tastes they are only infrequently used even there. But there is absolutely nothing unusual about using this style of music in church, and singing it in church was the original intention.