This is one of the risky spots of that guide. We cannot emphasize it enough on that one: clear the area before going in that hidding spot. Clear the houses and loot quickly if needed. You also have to ensure that the river is safe and use your scopes to check the West of Repulsor since ennemies there have a clear line of sight on you when you set up Octane's Launch Pad. A Bloodhound scan can reveal ennemies on top of the building if you are close enough but be careful if you reveal an ennemy team. They will very likely try to find you and fight.

In order to reach that cliff, you will need an Octane's Launch Pad. You can place it roughly where it is on the next screenshot. You will need a super jump to reach that spot: press your jump key right after you hit the Launch Pad and be ready to air control and climb when you hit the cliff.