This way, the spins are selections from a stream. If you take a number of samples you can guess the position in the stream and then calculate the most advantageous time to run another spin. The inputs are probably read on a 60hz timer anyway so you can predict which time you're going to get within a few ticks.
We can probably agree that PRNG is a function that takes an input and produces an output. I guess you take issue with me calling this input the seed. My use is probably a simplification indeed, but I thought one that doesn't change any principles. Because the user's interaction timing is crucial, it seems pretty clear to me that the exploit is about influencing the input of the PRNG. We can call this input something else, e.g. internal state. Or we can call it the seed.
Based on the article it seems that the flaw is that the machine uses the timing of human interaction as a significant seed source. This works well enough for unaware people, but as evidenced here is super easy to exploit once the knowledge is out there. Using time (e.g. the time the program started) as the PRNG seed is a very common security flaw. Otherwise experienced engineers keep making this mistake even in 2017.