I don't understand it either, lol. My neighbor is a yDNA I1a and has a DYS390-23 just like me and I'm an R1b.
"The J2 lineage originated in the northern portion of the Fertile Crescent where it later spread throughout central Asia, the Mediterranean, and south into India. As with other populations with Mediterranean ancestry this lineage is found within Jewish populations. Research note: Many people new to Genetic Genealogy think the J2 haplogroup is synonymous with having male Jewish ancestry. One should note that having a J2 haplogroup assignment does not necessarily indicate Jewish ancestry. The J2 haplogroup is far more ancient than the Jewish religion and is found in many lines with Mediterranean region ancient ancestry. Another relatively more recent mode for J2's entry into some parts of Europe from the Mediterranean areas could have been the Roman Legions and Roman settlements."