Just to be clear, this was a primary election within the pro state hood party (PNP), who tend a little toward the republican side, ironically given the national Republican’s party obstruction of consideration of Puerto Rico state hood. So even the democrats within that party will tend toward the conservative side. The other major party PPD is in general in favor of continuing the status quo as a US territory, or some advocating for independence with a free association with the US. This party tends to lean a little more toward the democrats.
Both of the two major parties have Democrats and Republicans in them though, and are more defined based on views of Puerto Rico’s status in regards to the rest of the US. There are also some significant larger additional parties.
Anyways, that was why both candidates are pro state hood, it’s the primary for the pro state hood party. And as someone else pointed out, Democrat vs Republican is too simple of a way to view the political situation.