About the only way I can think of is that there is a cartridge bearing that is a press fit into the very top of the headtube and the steerer is a press fit into the inner race of that bearing. The fits would have to be tight to keep the fork from dropping out of the bottom of the headtube if the front wheel is lifted.

Edit: I just saw FB's posting but i don't think the top cap in the photo is anything but a cover. The topcap of a threadless headset rotates with the fork and this one appears to rest on the stationary edge of the headtube. Also the cap is not at right angles to the steerer but it cocked several degrees relative to it as it looks parallel to the top tube.