Yes, that is correct. Listen to a recording of the style, try to imitate and practice this at home, when a song of that style arises in church try to apply what you learned of that style. The video you lined to is an example of this.
I'll clarify some terms:
SATB hymn - when all four vocal parts are written out in full across top and bottom staff.
Lead sheet - melody, chords, words. Usually single staff. Chords are not written out as notes (like SATB hymns) but as chord symbols. Eg: C, G7, Am7(b5). You may have heard the term "Fake book," these are written out as lead sheets.
Take the video example of an accompaniment style you gave. Using a lead sheet, you would follow the chord symbols for the accompaniment. The folk song example in the video may have the following:
A, E, A, E, F#m, D, Bm/D, F#m, D, A, Bm.
From there apply the stylistic pattern to the chords.
In order to do this you would need to be familiar with chords. There are chord books out there which give the notes for each chord symbol. (Make sure to get one for keyboard, as the guitar ones are different). You would be using this along with your scale book for reference whenever you do not know the notes for a chord or scale.