You quoted your own post and said that is correct so bear with me while I'm asking again because I don't even know how this could possibly happen.
1. You have a league in PB18 that is fictional and has no NBA history in the almanac
2. You're using the import PB18 league feature from the main menu of PB19 and not creating a new league
3. Somehow your imported league shows everything as it was in PB18 but now has NBA historical data with it too
I honestly don't even know how that would be the case because all the import does is copy your old files from one spot to the next and then changes a couple of fields in the data structure to account for new settings and such. If that is what is happening go to
www.wolverinestudios.com/support and open up a ticket there so we can collect your PB18 league files and see what is happening