Don't believe him!
US TV's are designed to work on a 110V electrical supply. The UK uses 240V.
Further, for the circuitry inside the TV to operate correctly, the power supply doesn't just need to be at the correct voltage; it has to be at the correct frequency. The USA system has a frequency of 60Hz. The UK supply is at 50Hz
US television transmissions use the NTSC colour system. The UK uses the PAL system (which is not compatible with NTSC).
Terrestrial digital broadcasting, in the USA , uses the ATSC system, referred to in your question. The UK uses DVB-T, which involves a different form of modulation and is not compatible with ATSC
Lastly, even if an ATSC tuner could decode DVB-T transmissions, the frequency range tuned by the American product might not be the same as the required frequency range for Freeview reception.
Chris