If airports with pilot controlled lighting share a CTAF frequency, could the lights be triggered at multiple airports?
In theory, this could happen.  The consequences may not be severe - wasted power, some light pollution, and a false impression from seeing the lights alone that an(other) aircraft is trying to use the airport when in fact it isn't.

However, it may be less likely than you think.

For one, an aircraft in the air, even at pattern altitude, is going to have a much better path of radio propagation to another aircraft in the air, than an aircraft over one airport may have to a ground antenna at another - in simplistic terms, the radio horizon has doubled.  Ideally (for example in planning towers for a cellular phone network) frequencies are not re-used within the range of expected propagation, but only beyond it - however, in the aircraft-to-aircraft case you have doubled that over the air-to-ground case.

For another, an aircraft receiver is designed to be able to pick up weak signals.  In contrast, the receiver and decider for pilot controlled lighting may have an intentionally high signal threshold, to only trigger on strong nearby transmissions, and not on distant ones, random radio noise, or weak harmonic interference from transmitters on non-aviation bands or unintended emissions from non-radio equipment.