It tells you what different types (in the generic sense) are in the radius.
The feature description says
For 1 minute per level of the spell slot you expend, you can sense whether the following types of creatures are present within 1 mile of you (or within up to 6 miles if you are in your favored terrain): aberrations, celestials, dragons, elementals, fey, fiends, and undead. This feature doesn’t reveal the creatures’ location or number.
Notice that it explicitly spells out that the location and number are not revealed, but it doesn't say that type is not.
That's not much to go on, but... this feature is just badly worded all around. What "within up to 6 miles" is supposed to mean is anyone's guess, and if we take the reading completely literally, because it says "and", the ranger might get a sense of presence only when every type is nearby. Like: "nope, you get nothing" in the situation where there's a beholder, an adult red dragon, an efreeti, a hag, a death knight, and Tiamat all hiding behind a rock. ("What?!?" says the party after they are all TPK'd. "Oh, there wasn't a celestial within a mile, so it didn't work", you tell them.)
So, I hope trying to parse it literally is right out. Given that, let's try to read it at least in a way that seems to meet the intentions and which has some use for the player.
Even with revealing the type, Primeval Awareness is very situational and costs a spell slot — a very limited resource for rangers. Having it not distinguish in this way would be a major limitation. If aberrations are the focus of an adventure, and yet it happens there is a dryad in the woods five miles to the north minding her own business, the ranger would be unable to tell. In a typical fantasy setting, it's easy to imagine that some creature of one of these types is within range at all times. That would drop the feature from highly situational to literally useless.
So, while the text is open to interpretation, I strongly recommend the slightly generous one.
It's not an official ruling, but 5E designer
Mike Mearls appears to agree, tweeting that while Primeval Awareness does not reveal location or number, it does reveal type. Or specifically, he was asked "It doesn't indicate location or number of enemies, what about types?" and answered
just type
and then followed up with a clarification that it just lets you know, for example, "undead", not specifically vampires or zombies.
This doesn't specifically spell out whether multiple types are indicated, but I think that's implicit in spelling out that it does reveal type, not just a useless "ping! one of the many possibilities is out there!" answer.
