Lockwood and/or the cript wroter might well have flubbed the pronunciation of Canopus, but the fact is Mitchell does say Canopius so it could well be something different in TOS' fictional universe. And since we don't actually hear Tarbolde's first name Mitchell could be repeating the name of someone not of Earth. And finally the Earth dating system (referencing 1996) is directly aimed at viewers so we can have a reference we can understand rather than Mitchell using a stardate. In universe Mitchell could say 1996 because he wants Dehner to understand exactly what he's saying and seeing she's from Earth than using an Earth date just facilitates things.
Episodes to follow in first season do tend to support the idea that FTL doesn't happen until at least mid 21st century and maybe a bit later. Indeed even in "The Cage" the idea is put across that the Enterprise
is of a breed of ships significantly faster than what existed before. We don't know the specifics, but the idea is put across.
The 2018 date from "Space Seed" suggests a new form of propulsion made the use of sleeper ships obsolete. My conjecture would be a fast relativistic drive that allowed crews to take advantage of time dilation. It might have been the development of impulse as we know it. That with artificial gravity (as referenced in TAS' "Slaver Weapon") means ships could accelerate more quickly to cruising speed and decelerate more quickly, too. Now you can get to other nearby star systems within a few years (objective time) while it's much shorter for the crews.
If Cochrane develops the space warp in the 2060s and they have fast STL ships since 2018 then thats an easy forty some years to get to other planets where either a human named Tarbolde travels to the Canopius planet or an alien with a name sounding like Tarbolde is encountered there and the traveling humans hear his poem translated and recited in English.