Is it fraud if my odometer was "rolled back" before I sold it?

I just sold my vehicle which had 72,000 miles on the Odometer. I didn't realize it was "Rolled Back" from 272000 miles until after selling it. I bought it from an auction as a "TMU" and had it for a year before selling it off again. I had another potential buyer who came to see it and was apparently upset that he never got the truck for the price it sold for and did a "Carfax" with the VIN and called me after I sold the vehicle to tell me I had just committed fraud....which scared the hell outa me! I did a Kelly Blue Book search for pricing of the vehicle at 272000 miles and KBB priced the vehicle out to be $500.00 more then what I sold the vehicle for. Which I'm glad I sold it for that price....by the way! So, my question is, did I commit fraud for not knowing the original miles. Did I do wrong to sell the vehicle? Do I have to tell the person I sold the vehicle to that the mileage was not accurate? Or....what do I do? Please ONLY reply if you know the facts!!! I really need to know!