ANSWER:
What they have said is absolutely baseless and fabricated.
It is not mandatory to pray as these are voluntary prayers. However, you would lose a great deal of reward if you don’t pray them but you’re not sinful and your prayers are valid.
Prophet salla Allahu alaihi wa sallam never used to miss Witr and 2 rakahs of sunnah of fajr even while he was traveling, however these are not obligatory.