Agree, I never understood that 'you have to be size this and this height to wear it' trope. I mean, in SOME cases that's true, but not in near as many as trotted out here.
I'm myself 5'11'' size 6 and my mother is 5'3'' size 16-18. We don't own this particular Alemais dress, but a few similar/same cut ones. I look fine in them and my mum looks fine too, she just (obviously) needs a bigger size and the dress shortened (or a petite version). And no, she doesn't look like a 'sack of spuds' either.
For what it's worth - I like the OP's choice. It's silk, so won't look like a beach dress. The flipflops make it 'beachy', imo. I like the pattern, creative and different. I think with the right shoes, jewellery and a clutch/bag it would look perfectly great and appropriate for both occasions. I'd certainly wouldn't bat an eyelid at anyone wearing it for my wedding. I'm a rather flamboyant dresser myself and don't judge others. Although yes, I wouldn't wear white to the wedding, but that's about it.