Not quite. He's on a planet somewhere in the Eye of Terror, hunting a Word Bearers' warband, who are building a temple. Think it's meant to be set, either during or just after the Scouring.
He's taking them out one by one, with the intent of drawing Lorgar out. Forms himself into a murder of crows that tears a marine to shreds, one of them screams over the vox and the rest are wondering what could cause a marine to scream like that, before they eventually scatter back to the portal, where Lorgar appears.
The warband are saying it's a daemon but Lorgar knows who it is, calls Corax out, who says something along the lines of "we are made of warp and now I'm in it, I've learned how to use it" before the two primarchs go at it.
Corax fucks Lorgar up so he runs back through the portal, ignores any of the Word Bearers and locks himself in the Church, and hasn't came out since.