Dr. Z plagiarizing or out of order

Case: Dr. J and Dr. Z (the former a microbiologist and the latter a biochemist) cooperated on a new medication. Dr. J published the article listing both their names with his own first in his microbiology journal. Dr. Z tweaked the data and findings, but in no way falsified, and published in a biochemistry journal but listed himself first in the authorship listing.
Questions.: Was Dr. Z plagiarizing or out of order? Why or why not?

Sample Solution