Canadian spelling is a hybrid of British and American. For example, centre not center, but aluminum not aluminum.
For this particular word (spelled/spelt), British spelling allows both forms interchangeably, with spelled mildly preferred in Canada but both may be found:
I wonder if there's an east/west variation on usage in Canada. Out west here I've only seen spelled (and other similar words with ed rather than t) used. I suspect the closer to the maritime provinces you get, the more British influence on the usage.
Perhaps they used the American spelling because they’re quoting an American?