NE-α parasite != European Plagas parasite.
This isn't what they said.
"Plagas is the
original basis for NE-a"
NE-a is Plagas-derived. Dunno enough about RE canon to say whether that was originally/explicitly always the case. Edit- Actually I'm remembering a little bit about this... the context for this may have been always there (Plagas as another "progenitor" virus.)
I don't think this contradicts RE4, at least in the way Nintex fears, since all that lore about the Plagas' history can remain intact even with this new info.