You did the right thing! Clipping off the dead, brown tip of a woody seedling will encourage growth and perhaps prevent the spread of a disease. I do not think your seedling is diseased however. My guess is the tip that is brown just did not sprout new growth so nature will seal off the unproductive tip to divert energy to the nodes below that are sprouting. Your young plant looks fine. Keep soil moist and air flow good during the warm spells. Do not get foliage wet to help prevent diseases. Keep growing, Marianne Binetti