A multi tap ballast is generaly understood to mean one that can work from a number of different supply voltages, but that this requires manuall selection of the correct wire or terminal by the installing electrician. Not automatic.
A smart ballast is generaly understood to be one that has only two input wires or terminals, that may be connected to any supply voltage within a range.
The internal circuitry adjusts automaticly to any voltage within the range. Nothing requires selecting by the installer.
The O/P however appears to be refering to neither of these, but to a fixed voltage 277 volt only ballast being worked from a 240 volt supply.
Although not correct, the difference is not that great especialy if the nominal 240 volts is in fact nearer 250.
It is probably running the lamp at less than the design power with the likelyhood of reduced output and problematic starting in cold conditions. In warm or hot conditions it is probably fine.
Arguably a violation to use equipment on the wrong voltage, but I doubt that there is in fact any danger.