No, I have looked at the evidence and I can think of no reason why the PJ wouldn't interview this man if he had contacted them on 4th May. Why would they not, when they were following all leads?
http://www.mccannpjfiles.co.uk/PJ/SEX_OFFENDERS_INFORMATION.htm#p1p134
http://www.mccannpjfiles.co.uk/PJ/NUNO_LOURENCO.htm
http://www.mccannpjfiles.co.uk/PJ/LANCE_PURSER.htm
Please correct me if I am wrong, but it seems to me that the PJ cherry picked which leads and sightings to follow. I know they were very busy, but this one could have been very pertinent.
...........
Right from the word go, did Amaral decide that The Mccanns had done it? Did he, or did he not, from day one say that he already knew who had done it ?
Did he neglect leads that might have proved otherwise ?
1) Because there were several sightings up in Porto that were interesting, that no-one ever mentioned other than in a non positive way. In fact, IIRC, two of them were rubbished. One sighting statement, from up there, was substantially altered by a new statement that overuled the first, which came straight from the "Horses mouths", a taxi driver and Police Officer on the spot.

The overruling statement came from Portimao Police who were NOT on the spot and changed the bona fide original statement in 5 ways.
2) According to Matt James there were well over 20 sightings in Malta (28 sightings IIRC), yet it appears that these were ignored

Did Madeleine in the first place, go by boat part of the way to Porto? I think she may have done.