Having doubts is never a result of concupiscence; neither is a mistake in understanding God’s will in any given situation labeled concupiscence… I think it is good to recall that the scripture tells us St. Joseph was a “just” man.
This is Father Hardon’s definition:
CONCUPISCENCE. Insubordination of man’s desires to the dictates of reason, and the propensity of human nature to sin as a result of original sin. More commonly, it refers to the spontaneous movement of the sensitive appetites toward whatever the imagination portrays as pleasant and away from whatever it portrays as painful. However, concupiscence also includes the unruly desires of the will, such as pride, ambition, and envy. (Etym. Latin con-, thoroughly + cupere, to desire: concupiscentia, desire, greed, cupidity.)
This in no way applies to St. Joseph, as I understand it. Nor do I understand that St. John merely questioning in a moment of doubt (if in fact, that is why he sent messengers to Jesus) could in any way be called concupiscence, as defined above.
The CCC also describes it in a way that does not pertain to either of them.
**2515 **Etymologically, “concupiscence” can refer to any intense form of human desire. Christian theology has given it a particular meaning: the movement of the sensitive appetite contrary to the operation of the human reason. The apostle St. Paul identifies it with the rebellion of the “flesh” against the “spirit.” Concupiscence stems from the disobedience of the first sin. It unsettles man’s moral faculties and, without being in itself an offense, inclines man to commit sins.