“It’s really important that the opposite is also true (two images that are not the same do not have matching NeuralHashes) because otherwise Apple’s system could falsely accuse people of trading in CSAM.”
Yesterday’s collision was built on purpose. This one wasn’t. A search of ImageNet turned up two pairs of ordinary, unrelated photos with identical NeuralHashes. Apple says it found 3 false positives in 100 million test images. Nobody outside Apple can check that, because nobody outside Apple can see the hash database.