Which aircraft was not on the centerline...Problem solved.
If both were then? Toronto Airport Authority is to be blamed.
If PIA aircraft was not on the centerline under marshal control (manual or electronic) then? The provider of this service would be held responsible.
PIC is the final authority but others also are liable under vicarious liability (duty of care).
These incidents almost exclusively occur due to pilot error, ramper error, not utilizing wing walkers, equipment failure, etc. ATC doesn't generally even have control of aircraft in gate areas; at busier airports, most gate areas are within non-movement areas. I can only think of a handful of times when incidents similar to this were even partially attributed to ATC.