The resistance measured between the ANT pin and Ground is low because of an inductor connected from signal to ground as part of the built in BALUN inside the chip. Please note that, this will not result in a short at RF frequencies.
For CYBLE-022001-00), the two components next to the ANT pin are used for matching the ANT pin of PRoC BLE to 50 ohms. The other two components are used for matching the chip Antenna's impedance to 50 ohms. For 2450AT18B100E, we took a deviation from the antenna datasheet because of space constraints and so we had to modify the matching network accordingly. But, you can choose to follow layout and matching recommendations the Antenna's datasheet also, if you have space for it in your board.