Where did you get that from?
They are not 2 separate issues. One leads to the other. Deca and tren, and specially their metabolites have progestagenic activity, meaning they bind strongly to the progesterone receptors leading to an increase in prolactin production.
So and making it short. Deca and tren activate the progesterone receptors which can lead to an increase in prolactin production, simple as that.