When you're moving through the peripheral vision of someone who's overwatched you, cover is checked for at the tile you moved from, not the one you moved to. That's why you can only do it for one tile (and why it can be done in the first place). It doesn't work here because the tile he moved from wasn't cover.
(by CyberBoy2000)
https://clips.twitch.tv/DelightfulBombasticRamenEagleEye-3J8dG2A-r3aYyA2K https://discord.com/channels/313015356052471828/642449134950940672/828192187862876171