Change internet interface?

Besides Openhab2, there is an access point running on my Raspberry Pi 3 creating an second WLAN (with different IP ranges). I did this from this tutorial:
My Pi is connected with my FritzBox over LAN. I can connect to openhab from booth WLAN. But if i try to Ping my Smartphone, it wont work. Only if my smartphone is in the second WLAN. Is there a way to say that openhab2 only runs on my LAN interface (eth0) ?

Sorry for my really bad english.