That is partly correct, but YTO does not mean Pearson. It means Toronto (literally). Same as LON represents London and NYC represents New York, but in both cases those codes represent no specific airport. YYZ is Pearson, and YTZ is the Island Airport (although I could have sworn this used to by YTI). Some carriers based in other countries use the more basic city codes as they only fly into one airport anyway, and it reduces confusion with baggage handlers when your luggage passes through countries where the code YYZ would seem to have no correlation to the name Toronto Canada. And if you happen to be a pilot, Pearson is CYYZ