Consider the 2. Concentration and the other thing.
Both bring stillness (among other things) but via 2 different ways.
It’s like making peace with your neighbors.
One way is to put up a big privacy fence.
The other way is to make friends with them.
I’m playing it completely straight here.
I’m using a metaphor to describe how the same thing (stillness) goes using the 2 meditation techniques, more or less.
To clarify.
Samatha (concentration) is like a privacy fence in that it shuts away the agitating stuff.
Vipassana (the other thing) is like making friends with the neighbors in that it sweetens your relationship with the agitating stuff.