> Afaiu the projection works with the weight update. But here the vector is getting added to residual stream from engram lookup not as direct updat. So the approach is little different.

Residual stream steering is what the authors do, the orthogonalized weights are downstream of that. Those weights, of an obliterated model, are all computed w.r.t. the computed residual stream vector. The original paper focuses on steering, but the community loves the simplicity of not needing to make changes at test-time.