Any transmitting device be it a cellphone or transciever not only transmits a
modulated carrier but also third seventh and mutiples thereof of harmonics. However miniscule these harmonics are, they potentially can interfere with the electronics of the
fuel delivery circuitry, and thus cause errors in fuel readings and/or pricing.
If interference did occur to the fuel metering (which is very unlikely but theoretically possible) it would be due to the fundamental transmission frequency rather than the harmonics, because (a) the harmonics will be several orders of magnitude smaller and (b) the metering electronics will be less sensitive to the higher frequencies.