There exists an entire industry for counting and sorting things(e.g. optical bean sorting).
There also are rather cheap optical tachometers(measuring rotations by applying reflective tape on rotating surface). I would guess such devices could also be tailored for counting falling objects.
And also there are multiple old- school tricks for similar tasks. E.g. if you need to count nails, weight them all, then weight a single nail, then divide the weights to get count.
This scales better. Also, going by the pictures in the article, the pearls are of varying sizes, so making a machine to count them would be a tad more tricky.
When you're counting things of uniform size and density (like screws or coins, one type at a time), the usual trick is to weigh them all, then weigh a single one, then divide the two numbers.
The new camera approach obviously is a lot more accurate, powerful and simple now once you have it.
But totally agree looking at their previous solution it feels extremely primitive. There surely must have been a simple middle ground without the app, using a mechanical funnel, a wheel or one-dimensional photosensor to count these. Even if they are different sizes and not always exactly round, the shape and size is still rather uniform.
There also are rather cheap optical tachometers(measuring rotations by applying reflective tape on rotating surface). I would guess such devices could also be tailored for counting falling objects.
And also there are multiple old- school tricks for similar tasks. E.g. if you need to count nails, weight them all, then weight a single nail, then divide the weights to get count.