Pearson has a variety of parking spots away from T1 and T3 for planes, that are assigned for operational reasons. Could be that T1 didn’t have room for another 777 in the international area. Maybe there was a minor security issue that they didn’t talk to you about that made them not want to bring it up to the terminal. Maybe TK got cheap.

Options for off-terminal parking include the infield terminal (gates 521-531). I’ve seen that used during construction, but was also used during the Syrian refugee airlift. I think what you got, however, was one of the parking spots (H1-H21) on the tarmac where the old T2 used to be. A bus from there takes you to a door in the basement at the end of the US/Intl pier, I think E83 or E84, and you get to walk to customs from there.