Help with this mitten pattern!

Hi, I am working on this mitten pattern , but I am stock in the part where I have to knit the thumb. This is what do not make sense to me:

Shape thumb gusset: (…)
11th row: K5. P2. K2. C4F. P2. K13. Inc1 in next st. K10. Inc1 in next st. Knit to end of row. 60 sts.
13th row: K5. P2. C4B. K2. P2. K27. turn. Slip rem sts onto st holder.

***thumb: next row: P16. turn.
Work across these 16 sts in stocking st until Thumb measures 21⁄4" [5.5 cm], ending with a purl row.

After row 13th, I end up with 18 sts in my needle, but to make the thumb I purl 16 sts.

Please I need your help interpreting this pattern!!

Thanks.

Here is the pattern link http://com.yarnspirations.pattern-pdfs.s3.amazonaws.com/Patons_ClassicWoolweb15_kn_mittens.en_US.pdf

Welcome!
Before the turn in row 13 you should have 18sts on the left needle and 42sts on the right needle. Turn and place those 18sts on a holder. You should now purl 16sts out of the 42sts and again turn. For the thumb, you work back and forth on these 16sts in stockenette stitch.