What it really did was take me up the off ramp, do a U-turn, and get back onto the on ramp to gain about 700m of distance from where I was before.
I'm pretty sure that isn't even legal, at least in the state of Washington. I rarely go that way, so help me out here Seattle-area Eastsiders, but a lot of folks used to do this on eastbound WA520 at 108th in Bellevue, to the point that there at least used to be a sign at the bottom of the exit ramp saying (in much fewer words) no, you can't get back on the freeway by going up the entrance ramp. (Sorry, street view doesn't show the sign that said, IIRC, "no reentry", so I could be imagining it.)