I've taken a close-up of the damages and a view of a good one (that is broken in some other way :-)
From the good one, R26 is the current sense resistor in the emitter line of the main switching transistor. The transistor is shorted B-C-E, so my guess is:
Some kind of unknown event took out the main transistor, this let the magic smoke out of R26 and did some more collateral damage (the controller IC lost a leg and vented through a pinhole, some other resistors are blast and one more transistor lifted its hat).
IMO the R26 event started the arc to the 5mm distant PCB trace.
No, the secondary side was not hit by the arc, there's no visible evidence.