Hello and hope you are doing well.
The major cause of coughing up blood is chronic bronchitis or bronchiectasis. Other possible causes of coughing up blood include COPD, lung cancer, tuberculosis, pulmonary embolism, pneumonia and lung abscess to name a few. Also, check to see if he is on blood thinners for heart disease, this could be causing the bleeding. I suggest he should go the ER, for immediate evaluation.
Hope this helped and do keep us posted.
He needs to go to the ER or to his doctor asap