We should probably remember that the seal of the confessional does not apply only if the petitioner is sitting in the actual, official "confessional" booth. It is a sacred duty pertaining to role, not physical position.
The McCanns could speak freely (as any of the rest of us could) to a priest, and it would be considered within the sacred confines of each respective role.
This is a key difference between pastors of the Protestant faith and Catholics: Some Protestant ministers/pastors might regard themselves as "off duty" at certain times, such as when they are with their families. Not all of them, certainly, but some would be able to say, I am within my role as husband/father, I am not acting as pastor right now. For example, a Protestant pastor might feel quite free to reject a call to another church, or a direction to move, even if it came from church hierarchy.
Catholic priests, on the other hand, consider their role to be a 24/7 thing. There is no time at which they are not subject to the call of the Church. A directive from "higher up" is a directive from God and accepted as such. Priests do not retire.
My favorite illustration is of this is an anecdote about a particular Jesuit priest in seminary, Father Browne, who happened to be aboard the first leg of the Titanic on her maiden voyage. A wealthy couple traveling had enjoyed the company of Father Browne so much they asked him if he could continue the voyage with them. The priest telegraphed the Vatican for permission, and was given the immediate response to get off the boat and continue with his regular assignement and duties.
As a dutiful priest, Father Browne did so, and went on to serve with heroic distinction as a chaplain in WWI. I'm not sure I wouldn't have said NO WAY! to the telegram, enjoyed the beginning of a luxurious cruise, and gone to an icy and swift death very quickly!
My point is that while some of us would regard earthly justice as an essential thing, it is quite possible that this Portuguese priest feels most at peace leaving that to the will and further actions of God.
As well, even if the McCanns said or did nothing that raised his suspicions, he might also be a very sensitive person who, being very sincerely devoted to the needs and emotions of others, might have found dealing with their situation a very traumatic one.