Aren't owlbears pretty much the archetypical "A wizard did it" monster?
Owlbear = post it note. Created en passant while trying to make a Flying Monkey+1.
Next question for the Faerun Visitor's Bureau:
How many tieflings live in the city of Phlan?
Is it plausible that there are zero? that no tiefling has ever set foot there?
Is "ten" a plausible answer?
How about a hundred?
When it comes to most fantasy worlds such as what is found in D&D... people interact all the time with so many different races that any one particular one I personally would not imagine elicits much surprise or response. Even if someone sees a tiefling in person for the first time... they know of tieflings already, and have seen so many other people of varying races that this new one wouldn't be that much of a concern. And even if there was a chance that seeing a tiefling would be a "shock" to someone in Phlan... the Phlan citizen would most likely be able to mask that shock with a civil face and reaction.

(Dungeons & Dragons)
Rulebook featuring "high magic" options, including a host of new spells.