The idea that you bought an ugly proposal ring or chose a bad location and it made the girl say no never occurred to me, but it's a terrifying thought.
For some girls, yeah. But the real issue was a lack of clarity, even if she focused on a big dramatic proposal. If he had explicitly asked about marriage it would've been a pretty good proposal.
Don’t worry if she says no just because the proposal sucks though. Just have an honest conversation about your future and if your bad proposal caught her off guard, ask about what she'd like.
(I liked how he offered to pick the ring together and really, that should be normalized. It’s a lifelong accessory! Plus, the idea of finding a good pair you both like is romantic in itself.)