I too am working through the tutorial which appears horribly out of date (here yet another 5 months later). Not sure how anyone gets started using appium with it like that - hopefully it isn’t a dead project. Anyways I found you have to add another parameter to the appium.txt file that contains the device name as reported by adb. So, first run
adb devices
Then take your device name and add it to the appium.txt file like this:
[caps]
platformName = "android"
deviceName = "emulator-5554"
app = "./api.apk"