What is the authenticity of the following narrative? Why were Muslims asked to be different from The People of The Book - is there any context to this narrative?
حدثنا زيد بن يحيى، حدثنا عبد الله بن العلاء بن زبر، حدثني القاسم قال: سمعت أبا أمامة يقول
خرج رسول الله صلى الله عليه وسلم على مشيخة من الأنصار بيض لحاهم فقال: يا معشر الأنصار حمروا وصفروا، وخالفوا أهل الكتاب . قال: فقلنا: يا رسول الله، إن أهل الكتاب يتسرولون ولا يأتزرون فقال رسول الله صلى الله عليه وسلم: تسرولوا وائتزروا وخالفوا أهل الكتاب . قال: فقلنا: يا رسول الله، إن أهل الكتاب يتخففون ولا ينتعلون. قال: فقال النبي صلى الله عليه وسلم: فتخففوا وانتعلوا وخالفوا أهل الكتاب . قال: فقلنا: يا رسول الله إن أهل الكتاب يقصون عثانينهم ويوفرون سبالهم. قال: فقال النبي صلى الله عليه وسلم: قصوا سبالكم ووفروا عثانينكم وخالفوا أهل الكتاب
"According to another narrative of an incident, as reported in Musnad Ahmad ibn Hanbal, Abu Umaamah (ra) reports that once the Prophet (pbuh) came upon a group of old people of the Ansaar with beards that were completely white. He said to them: ‘O people of the Ansaar, dye your beards red or yellow and (thus) be different from the people of the Book. [Abu Umaamaah says:] I asked: ‘O Prophet the people of the Book wear [clothes like] pants and avoid wrapping the loincloth, [what should we do?]’. The Prophet (pbuh) said: ‘You should wear [clothes like] pants as well as wrap the loincloth and [thus] be different from the people of the Book’. I asked: ‘O Prophet, the people of the Book walk bare feet and avoid wearing shoes, [what should we do?]’. The Prophet (pbuh) said: You should walk bare foot as well as wear shoes, and [thus] be different from the people of the Book’. Then we asked: ‘O Prophet, the people of the Book keep their beards closely trimmed and let their moustaches grow long, [what should we do?]’. The Prophet said: You should trim your moustaches and let your beards grow and [thus] be different from the people of the Book’."