100% false. I just did this myself with 2 large green, a large red and one baby (I had two babies but they glitched on a hill and one died). I got them to follow me all the way to a monster crocodile.
It took a while but it was fun.
And considering the fact that I can only get 4 creatures to reliably follow me, I’m assuming the person on your server did this legit.
After dropping the dragons off with the croc, one red and one green left immediately.
The baby died very quickly and it took 20 minutes for the monster croc to kill the remaining green dragon; it still had about half of it’s life at the end. So no wonder that guy took two large ones to kill it.