As noted, Tieflings have been part of D & D lore for decades now - in fact one of the potential companions in BG1/2 is a Tiefling Bard. Their presence in larger numbers is again due to current D & D lore, involving Elturil. However, Larial could certainly throw in some in-game conversation content in which the Player can obtain more detailed information about this race from Volo, druids, tieflings and even shop keepers. They could even sprinkle a few cooks containing relevant lore around the grove 0 again maybe Volo has been putting something together you can look at.
In -game observation of tieflings should show you they are more familiar as a race (jobs, family structure, fear of dangerous critters eating their kids) while discussion with your Gith companion certainly reveals their race to be more "alien" in culture.
As for Drow, again D & D lore going back well over 20 years establishes there have always been a variety of different drow groups - those following Loth, Shar and the Seldarine as some examples, Breggan D'arth (yeah, probably misspelled it) as another group. Again, current lore has them interacting with the more common surface races more often now than in the past. And if a group of adventurers that happened to include one drow elf just saved my town's bacon by aiding in it's defense, I think they might be given the benefit of the doubt - such benefit was certainly provided to the infamous Drizzt often enough. And Drow criminals can be anything but common - Breggan D'arth as a criminal and mercenary organization is right up there with the Harpers and other such organizations in terms of ability and influence.
You may prefer your drow evil and arrogant, while some of those evil, arrogant drow might prefer their player characters be served with fava beans and a nice chianti. And there can now be arrogant GOOD Drow to tick you off as well.
