Am I rude for telling it to my mom?

My sister said she ordered an original converse from her friend which cost about $4 and her friend said she would buy it in mall and its original like brand new and I just assume its not original so I told my mom it might be fake cuz original converse costs about $50-$100 My sister overheard it and called me bigmouth.
Am I rude for telling it to my mom?
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