If I understand correctly (and I might not), these optical switches work by interrupting a beam of light that passes through the center plastic cylinder / “pin” at the bottom. The center post of the stem is what interrupts the light as it travels to the bottom of the center pin. IF that’s how these work, all they’d need to do is install their dampened stems in lieu of normal ones. In fact, looking closely at the silver one on their page, it looks like the little rubber pads are visible:
In the other photos the circled area is the same color as the rest of the stem, but this one appears to be white in that area, which is the same color as the dampening pads that Gateron uses.
In my experience, Gateron silents are indeed pretty quiet - roughly on-par with something like a dome keyboard - and since these won’t have any contacts, these will likely be even more so.
Edit: two things I find curious - one, the travel distance you mentioned. Two: the resting position of the pictured switch. In the past, Gateron’s silent switches have had a higher-than-normal resting position, with the rectangular portion of the stem poking up above the housing - here they appear perfectly flush. This makes me think that these top housings are relatively new, and possibly revised to improve the performance of their silent stems.