There's some semantics involved here and how words are being used. Human generally is synonymous with Homo Sapiens, even before we knew what that was. Debating whether an indigenous person was 'human' or 'other' was based partly on ethnocentrism and the unknown. Especially if you paid attention to some of the literature at the time, Europeans were Expecting to find 'intelligent' 'human-like' beings, that were not actually human. Expectation can have a huge impact on what one sees. Ever hear of the Monopods?
Now, there would be a bit of a difference whether the races have known of each other for a long time or if they suddenly 'discover' one another.
If they've known about each other for a long time, then they 'know' how the other is. They might get along fine, or have just as much trouble as different human nations warring back and forth all the time, with periods of peace and trade. Dwarves and humans could live together fairly peaceably (as much as any human group can live with another) since the dwarves might live underground and the humans above, and the trade would be very profitable for both.
If they suddenly met and discovered each other, it would depend on several factors, how 'alike' are they to us, how powerful do they appear to be vs. us and how aggressive are they in general. If we feel mildly threatened by them or
superior relations might go as well as they did for the South Americans. If they are more powerful, we would treat with them trying for goods and allies against others.
Now for classification, we of course are humans, 'friendly' races are first individually identified (dwarf, elf, halfling, etc.) then would be identified as friend or foe, us or them. Though we would also likely come up with a term that equates to 'sentient races'.
If we discovered a new race, we have two starting points. One, we already have met some, Knowing about elves and dwarves and then meeting Halflings or not knowing any and discovering a completely new race.
The second situation would be much more like how we treated any new race we met in the past, Americas, China, Japan, Australia etc. Depending on their abilities, often the discoverer is more advanced (technologically) than the Discovered and they are then looked down upon as a lower life form. If we already knew some before, then our reaction would be tempered by what we knew of the other races. If we've only known kind elves then meeting rabid orcs might not go well the first go around, or vice versa.
But anyone we don't get along with will not be 'human' but dirty animals, and friends would be friends.
I wrote a lot, but I'm not sure I really answered the question.