I watched the interview with CP&S here lasting some twelve minutes until the King and Queen came on.
Prince Carl Philip: "I proposed at a secret place" | Royalista
Despite my reservations about Sofia, which I still maintain, I tried to look at the interview as unbiased as possible.
It came across as positive.
Sofia left an impression of being very happy, giddy and as such a little girly, while CP was more reserved or perhaps had more routine.
She didn't say anything silly.
The mistake was perhaps that they stood too close to the press, which meant that the cameraangles were shifting and unsteady and combined with CP&S physically having to turn in order to face whomever was asking, it left a messy impression.
Had the setting been more organised I believe the general impression would have been better and Sofia would have had to pose with engagement ring so much. (I know that annoyed some).
That the proposal took place the same morning may not be implausible. The arrangements and okaying in regards to the Riksdag and Regent Couple could have already been in place so that Sofia was simply surprised.
Conclusion: CP&S did fine, the PR handling was too improvised.
ADDED: I noticed someone else who said something about Eccentricity not being uncommon among royals and that Sofia might be seen as such, an eccentric figure.
I don't agree. In our day and age, where appearance counts for a lot, eccentricity is a luxury in royal families that are generally popular and resected. In such family the odd excentric family member may be seen as refreshing and even endearing. The SRF at present do not have that luxury.