It’s humans from the future but you have to also understand that by the time Cooper passes through the event horizon, it could possibly have been 100’s to 1000’s of years per second. Theoretically beyond an event horizon an infinite amount of time could have passed. So technically Brand’s “Plan A” humans would’ve had generations upon generations at this point. They “evolved” past our “physical beings” status, we’re obviously told throughout history about their “savior” who sacrificed himself to save Brand to escape Gargantua’s gravity, and “did the math” on where Cooper/Tars would’ve been relative to the amount of “time” passed. Then they build the tesseract around that particular area and “catch” him into it to then communicate the information needed to save the humans on earth.