Why did Jesus (peace be upon him) address the Prophet (peace and blessings of Allah be upon him) by his name plainly, despite the Qur'an forbidding that, and is that considered a sin or an exception for Jesus, and does that mean that Jesus is not concerned with following the law of Muhammad (peace and blessings of Allah be upon him)?

The intended hadith was narrated by Abu Hurairah, may Allah be pleased with him, in two versions. The first version does not include the phrase about Christ calling out to the Prophet, peace be upon him, in his grave, while the second version does. The first version is the wording whose authenticity from the Messenger is undisputed, whereas the second version was exclusively narrated by Sa'id al-Maqburi, and its narrations varied, and its chains of transmission are not on the same level of authenticity as the first version due to containing weakness or tadlis (deceptive narration). Al-Hafiz Ibn Asakir weakened the problematic wordings. In summary, the wording whose authenticity is definitively established does not contain the problematic phrase. Assuming the hadith is authentic, it is probable that what is meant is Isa (Jesus), peace be upon him, greeting the Prophet, peace be upon him, and his returning the greeting, which is established. It is not correct to build upon wordings whose authenticity has not been verified, especially since the Prophets, peace be upon them, are the most perfect of people, and when Isa, peace be upon him, descends at the end of time, he will uphold the Shari'ah of Prophet Muhammad, peace be upon him, and rule according to his Sunnah.