The app is correct. Night time is from sunset to sunrise. Landings are considered night starting one hour after sunset to one hour before sunrise so it's possible to log night time while logging a day landing. Go to the Notes area of the Leg in question and you'll see the sunset time. You should have landed within the one hour after sunset.
I asked this same question a while back after I landed in pitch black conditions following a redeye. Turns out I landed within an hour of sunrise so technically based on the FARs the app is handling this correctly.