I see the confusion. I think I've got it....
The legend should show an oval for the second yarn over instructions in the legend. There's no difference in how you work it on the RS, just a yo when you see a circle or oval. The difference is on the WS: on the WS rows (the even rows not shown in the chart) you purl every stitch but when you come to the oval's yarn-over, you work two stitches into the yo (p1 and k1). That's the only thing you need to hold in your mind. Purl the wrong side, and p1 and k1 when you come to a yo that's an oval, which will be almost all the yo's you come to. The regular circle yo's (only done at the beginning or end of row) just get a single purl stitch into them on the WS. That's the only distinction. On the RS the oval and circle are treated the same, just a single yo.
I hope that's clear.
If you want to confirm it with someone whose made it, you could email this woman who just made that sweater on her blog (bottom of this page).
Have fun! It looks like a neat pattern!