when i attached svellsongur to yasuo windrider i win 2 points when i move 3 times

Yes, that's correct — with Svellsongur attached, Yasuo, Windrider scores 2 points on the third move.

Svellsongur copies Yasuo's text box into its own Effect Text, and Effect Text abilities are appended to the rules text of the unit it's attached to (Rule 136.2.c). So Yasuo has two separate instances of "The third time I move in a turn, you score 1 point," and the third move satisfies both — each triggers independently and each scores 1 point. This matches the established Svellsongur pattern (FAQ #2061 with Ahri Alluring, and #9095 with Aphelios, where the copied ability triggers alongside the printed one).

Two notes: it's 2 points on the third move only — not 2 extra on every move, and not more than 2, since each instance triggers once. Those points aren't restricted by the once-per-battlefield Conquer limit or the Final Point rules, so they can also be the winning point.