Does a simple wire antenna need a 50 ohm transmission line?
The reason for using a consistent impedance from the RF driver to the antenna is to avoid reflections and so improve standing-wave ratio (SWR).
The impedances don't 'add' together, transmission lines don't work that way. Rather, the 50 ohm line continues on to the 50 ohm antenna as smoothly as possible (that is, without impedance discontinuity), so that maximum power transfer is achieved (that is, lowest SWR.)
If possible, if the chip / module vendor provides a reference layout, try to follow it exactly, using the same geometries and stack-up.