Impedance-matched antenna with an extra capacitor
It could be a cheap band pass filter. Self resonant frequency of 10pf is roughly 2.5 GHz. See this for example http://psearch.en.murata.com/capacitor/product/GRM1555C1H100JA01%23.html

It passes the wifi band nicely but attenuates the harmonic frequencies. If there is a problem with the harmonics, this trick could attenuate them a few desibels and make it comply to regulations.