I believe you are right, but the €95m total sum were definitely reported a month ago in Germany, that split in 90+5 seems to be a newer development, maybe a (admittedly small) offer from Dortmund to close the gap.
You are correct. Before the season ended, Sancho's price was touted as 95 million Euros (excluding bonuses) by the German media outlets, which was a drop from the 120 million Euros (excluding bonuses) last summer. When United started their negotiations with Dortmund, we got a new development last week, which was that Dortmund dropped the base price to 90 million Euros and are okay with a low bonus payment of 5 million Euros.
This indicates that the negotiations have progressed well for United, which is why both they and Dortmund were noted as being optimistic. United's lower official offer was obviously not near the 90+5 that Dortmund wanted, and that's where we are at this time.
We shall see if the 90+5 is the final price or if United can take it lower, but as it stands, United seem to think that they can drop this even further whilst Dortmund want to let United know that it won't go any lower.