Do you have a source for that?
I just consulted an online dictionary, a printed dictionary, a second printed dictionary, a Latin dictionary (because hybrid is a Latin word), and wikipedia.
The online dictionary says, "the offspring of two animals or plants of different breeds, varieties, species, or genera, especially as produced through human manipulation for specific genetic characteristics."
https://www.dictionary.com/browse/hybrid
All the other sources said more or less the same thing.
So if you have a source that says a true hybrid is a crossing of two species, I would like to see it, because I sure haven't seen it yet.