Hi thanks for your question.
Since your chest X Ray
is normal there is nothing to worry.Yes your right this could be due to dry condition.Spitting up or coughing up of blood could be due to local inflammatory process in upper respiratory tract(nose or pharynx) due to cold
.Cold causes vasoconstriction
of vesscels in upper respiratory and damages small vesscels,resulting in small haemorrhages which comes out with cough
Hope this answers your question.