The near-humans of Draenor are an in-universe speculative race used by Garona and Medivh to interpret the former's non-orcish heritage. In The Last Guardian, Garona makes various statements that there was a different group of humans living on Draenor than those the orcs later discovered on Azeroth, who were possibly rendered extinct some time before. When first explaining this to Khadgar, Medivh surmised that her homeland had "humans, or near-humans, or at least had them within living memory." Later on, Khadgar saw a vision of Gul'dan's quarters on Draenor, in which he kept "preserved things, some of which might have once belonged to human or humanish creatures" inside one of the cabinets along his walls. They were similar enough physically, mentally, and culturally for them to give Garona insight on humans of Azeroth, discovered through the newly opened Dark Portal.
Garona believed that she was half-orc and had half-human heritage from these Draenor-born humans. According to her, it was Medivh who "made [her] feel human. And [she hadn't] felt human in a long, long time." She specifically stated that she was "of both Orc and Human lineage" and "neither." Orcs only "[saw] the parts of [her] that [were] human;" they said her "human hand" was "too slender to be really useful, [did] not [have] enough muscle to hold an ax or bash a skull in properly—too pale, too weak, and too ugly." However, it was later confirmed that she is instead half-draenei, but was deceived by Gul'dan to believe that she was half-human.
While no specific Warcraft definition has been given, in other fantasy/sci-fi (ex. Star Wars & Doctor Who), near-human has meant a race that evolutionarily diverged from humans (or have mixed ancestry with other species). In some cases the term is used to describe a race that evolutionarily converged into a species biologically related to humans. Often humans & near-humans are genetically compatible. This term is synonymous with the term "demi-human" or "metahuman" and sometimes half-breed or hybrids from other fiction.
The revelation of Garona's half-draenei heritage would not explain the Draenor humans in a satisfactory way. It does not take into account the contrasts made between Garona's appearance and that of other half-orc/half-draenei by Brann Bronzebeard, the visions of human-like preserved corpses seen by Khadgar, or the fact that since Draenei (including Lost Ones and the Broken) are not even remotely human physically, mentally, or culturally (but perhaps spiritually), Garona wouldn't have been able to gain insight on humans from their more alien mindset. This would imply that either Garona grew up within a Draenor human slave camp where she learned their culture and thought she was one of them, or that her mother was half-human/half-draenei.