Perhaps it was from the same batch of manufacturing, which had some kind of defect in the process itself. That'll result in a consistent flaw across most devices produced in that run.
How QA generally works is, every Xth product is taken off the assembly line and tested. It's entirely possible that the products they did take out for QA passed the tests (as unlikely as it might sound), and the products in between were mostly defective. There's an element of luck as well, or the probability of a particular product being defective based on the QA testing, manufacturing process, etc.
RMA's help that process - if it's a hardware problem, they can narrow down the problem if they have the defective product with them. If it's a software problem, the issue can be isolated and fixed in a future driver/firmware update.
And as already mentioned, every single "high quality" peripheral has the same issue if you google "product name + problems/RMA/defects" - you'll always get the odd disgruntled customer having a string of bad luck, while the customers who don't have any issues whatsoever remain quiet.
