Would have expected ammonia to be at 0ppm if nitrite is at 0ppm.
Could be a false reading of ammonia.
Did you double check the tests, do one more check of ammonia as it’s quite common to get false readings especially if made a mistake with number of drops of solution from bottle to test tube.
Also any water sample taken from tank is less than 1 inch of water surface can be a factor, always best to get 5ml sample of water from at least 2 inches below surface of tank water, this way you get a purer sample as water surface scum from can have an effect on results.
I use a clean turkey baster to get water sample from at least 3-4 inches under water surface, saves getting my hands and arm from getting wet as well!