Welcome to the world of humanist typefaces. While the stroke thinkness es similar to grotesk fonts like Helvetica the letters are much more open. Just take a look at the lowercase e or the uppercase C or S.

If you take a closer look at the work of Adrian Frutiger you will spot some reaccouring patterns. Like the horizontal stroke of the uppercase G or the vertikal mirrored symetric k strokes. You can find these at the more geometrical Avenir as well.