You're right it's not good writing, but I think you hit the nail on the head in terms of believability. Whether an escaping Facehugger, an Egg onboard the dropship itself, or something grew under the flooring it does not matter for the story ultimately, it's a f**king Alien.
Although I will say:
We see something like this happen just before the Queen takes Bishop, where did the acid come from?
The womb, from the way the Queen violently tore from the ovipositor, so the idea that acid and fluids also contained zygotes makes sense.