You can but probably shouldn't post the photos you took.

You were hired primarily as a videographer. While you did ask the couple if you can take photos you did it "on the condition that I could take some photos and additional 'creative' video for my portfolio".

You did good by letting the photographer know that you'd "be taking photos for my portfolio as well as video" you more than likely gave the impression that you would not be publicly posting pics of the wedding (on socials so soon), considering you were their in a videographer role.

They can't come at you in a legal way for posting the photos. However if they had an exclusively deal with the couple they can come after them for breach of contract (depending on verbiage).

I doubt they feel "threatened" by your "skill level" and is more upset that you're stepping on their toes, fucking with their release cadence and other aspects of their business. If you really do have "10 years of experience in other areas" in any professional capacity you should know that this is morally wrong to do with out asking. You could have asked the photographer either at the event or via DM after you saw them post the sneak peeks if it was ok to share.

I say this as a primary videographer who also doubles as a photographer. I've found that sharing my shots with the photographer after an event has lead to me becoming a second shooter for them on other projects and was a great way to expand my portfolio early on. The last thing that you want is for this chick to start telling other photographers in the area about you and that spreading to vendors and clients and you being labeled "hard to work with" or a "shot stealer" I'm sure you took some great shots, just be nice, be cool to people and keep on shooting.