There are 2 other gateways within 3 km around yours though those have been offline since December. And quite a bit more when extending the distance. So yeah, maybe other LoRa(WAN) transmissions are to be expected. Of course, antenna placement will be crucial; see Best position for a gateway.
You might want to join the Athens community; maybe someone can tell you if your area should indeed see a lot of traffic, or not.
Note that the gateway’s Traffic page in TTN Console does not show historical data; it will only show packets that are received while you have your browser open. But indeed the total counter will show you how many LoRa packets have been received (even if not LoRaWAN, or if not TTN).