First of all - big hugz
as a past heavy smoker - I started stealing my dad's cigs at about 7 and started smoking regular around 12/13.
the lining of the lung becomes irritated and this can result in phlegm that is tinged with blood.
regular coughing can abrade the lining of the bronchi and throat and again this can result in phlegm tinged with blood.
both of these cases require him to re-assess his current lifestyle but they are not instantly life threatening.
If possible try to talk to him about this without becoming frantic or emotional - I know that can be really hard, but the more he see's you emotional or upset by it the more likely he is to close up.
try to remain as calm as possible, ask him to seek advice.
it could be a minor lung irritation or infection that is easily treated.
on another note - I do not condone or suggest anyone does this by the way - but my paternal grandmother has smoked ciggarettes since her early 20's, she is now 83.
My paternal grandfather has smoked since his pre-teens, mostly a pipe smoker, he also smoked the old woodbines as a kid. He is 81 next month.
My dad has been a smoker since his early teens - he is 55 now.
Smoking only increases the risk of heart and lung disease - it does not guarantee it will happen.
years ago my grandfather quit smoking and soon after developed pnuemonia. His doctor actually advised him to continue smoking his pipe and he has been illness free since. (like I say I don't condone it and I don't suggest anyone does it, my point is that people can smoke all their lives and not suffer from smoking related disease).
Speak to johnny, see if you can discuss things and ask him to at least seek medical advice. because the reality is that it could be something but just as much it could be nothing.