Confusion about the Injection of electrons and electron holes in a BJT
You're correct. A hole is a place where an electron could be, but is not. This has to do with the quantized nature of energy/charge. When it comes to charge flow, there are no positive charges, just lack of negative charges. So the term, hole, is a much more convenient way of saying that. 

So, anytime you read "injection of holes" you know it means "ejection of electrons". You'll likely find though, that when discussing it or thinking much about it, it's much easier to think of holes as being the things that push electrons out of the way. Hence the creation of the concept.