You actually can't tell what he used.
Board software converts a series of n-dashes into m-dashes. Did the experiment yesterday, I'll repeat it for you.
I will post 1, 2, 3, 4, 5 n-dashes and you can see what they are converted into.
1 -
2 –
3 —
4 —-
5 —–
6 ——
7 ——-
8 ——–
→ it also converts two n-dashes + into an arrow, try it you'll see.