@Tailikku. They're animals native to Dimension X that first come from meatball-looking eggs. They hatch the moment they're heated up, and little red reptilian critters pop out who feed themselves and are capable of burning thigs by hand.
Their main destination is water which they quickly become the yellow monstrosities seen here once soaked in.
In the episode they appeared in, it's revealed they can be defeated by electrocuting them which turns them back into eggs.
The only reason they're called "Pizza Monsters" is because they were put in pizzas as a trap for the Turtles to blend in with the toppings. (And they eat the entire pizza very quickly the moment they hatched out of their eggs)
So them being a reference to Alien would mean they were meant to hatch inside the Turtles' bodies and burst out while eating!

Pizza Xenomorphs?