The bit they are using in that picture has a bearing on the top part that is sticking out of the table (which is actually the bottom of the bit, because routers are inverted in a router table). Bits with bearings like that are safe to operate without a fence, because the bearing spins, acting as a guide as the stock is pushed along the bit. It doesn't matter which angle the stock approaches the bit from, because the bit is symmetrical, and as soon as the stock hits the bearing, the bit will not be able to cut any deeper.
The bit in the picture is known as a flush trim bit. In a router table, the bit can be used to trace a pattern. In the picture, the pattern is provided by the Woodpecker's jig. The curve of the jig will be cut into the work piece. As the work piece is pushed into the router, the bearing is pushed against the jig template. Because the cutting blade is flush with the bearing, the pattern the bearing rides against will be cut into the work piece.
If that is difficult to picture, it may be helpful to view a video of it being done. Here is one I found on YouTube.
Bits without bearings generally require a fence to use. With no bearing, there is nothing controlling the depth of the cut. The fence does that for you.