I agree,
I suspect YYZ was good for TC B757 maintenance cover, a relatively minor failure but makes good sense not to fly it back to the UK ETOPS, so :-
A sensible decision to divert YES
A sensible diversion airport YES
Spot on.
BTW. The crew were instructed to fly YYZ for logistical reasons & speed of maintainence / Pax handling availible at that moment in time. Again, Aircraft was fixed within 1 hour & departed with minimum fuss. Great job by engineering & all concerned at Pearson.