If a Fully Enlightened, Sammāsambuddha, could make mistakes then he would not be a Perfect One. Imperfect beings can easily misinterpret his teaching due to their partial understanding.
The Vinaya rule prohibits a monk from lighting a fire to warm himself, and for no other reason. There is no offence if he is sick. To practice forbearance to forestall the arising of attachment to sensual pleasures, and to maintain frugality out of compassion for one's supporters who pay the bills is not self-mortification. However, one should not go to such extremes that one becomes sick. If one gets sick, then one will be a greater burden on supporters.
The Buddha did not intervene to prevent the suicide of some forest dwelling monks, because he knew that their past kamma was so severe that nothing could prevent it's bearing fruit. Likewise, he did not intervene when Moggallāna was being beaten to death by hired thugs. In the case of Angulimāla, the Buddha could and did intervene to prevent him committing the heinous crime of killing his own mother.
• • • • (Upasampadā: 24th June, 1979)