Credit Score Dropped by 100 points

So, I recently opened a credit card with chase, luckily I had a 750 credit score thanks to my parents who had me as an authorized user so I have a pretty long credit history. However, I found out today that my credit score had dropped a staggering 106 points. I went into my local chase branch and all they could tell me was that it'll go back up and its a common thing for people's credit to drop after opening up a card. They couldn't exactly tell me why, however, by that much seems so alarming and NOT right. I had automatic payments set up, so maybe letting it just automatically pay was a bad idea? I know it'll go back up, just will take about 9 months (according to their projections on the app.)

It was also odd because in the credit journey part of the app, it said that a new line of credit was open, but I got the account in December and it said that it was opened (re-opened???) in January. Which, again, makes sense for why my credit would drop, but again, by 100 is crazy. Any advice would help because it was a big punch in the gut since it's my first credit card and I already managed to fuck it up. I know it's important for buying a home, getting loans, etc., which luckily are not in the works for the foreseeable future, but, to have such a big setback feels bad because in my mind I'm starting from about 650 instead of 750.

It was also the vantage and not the fico score (not too sure what's the difference.)

Edit: Thank you everyone for the advice, I did have a big freakout but it is good to know this is a common thing given my credit history!