@ngroberts15 in case you are wondering who is right, both @MarkT and @DrDiettrich are right.
With wires in the air, it is a antenna.
The I2C bus was not designed to go through a cable and it was certainly not designed for twisted pair. Talking about a signal cable with I2C makes me frown, since the I2C bus is not that kind of bus.
However, when SDA and SCL have a accompanied GND wire, they are many times less vulnerable for electric noise. You might have to lower the clock speed of SCL because of the increased capacitance.
Did you see the picture in #26 ? That is in the I2C standard, but it is not perfect. Since SDA and SCL are not just digital signals, because they also carry a current. That means that the VDD is no longer the exact match with VSS and they don't fully reduce each others noise.