I mean, this is totally out of my area of expertise, so I’m just like a noob reading National Geographic or something, but my understanding is that it hit at an oblique angle, and that the moon has, or is made up of a lot of the earth’s mantle, which is less dense than the entire earth. The whole thing is just so incredibly freaky to imagine - basically two planets crashing into each other like that, the amount of energy involved is mind-boggling.
Off the top of my head, I think they’ve identified two galaxies crashing into each other somewhere out there. Although the timescale involved is hard for a human, like me, to even comprehend.