There's another stitch on the other side of the marker. Most patterns don't tell you to slip the marker, but you always do. They're just there to show you where to do the increase and this pattern just ignores them in knitting the sts. Think of it as "knit to 1 st before marker, m1, k1, sm, k1, m1" which is the same thing - you do 2 knits between the increases. It's less wordy to say 'k2' rather than 'k1, sm k1'.