How to understand this clause about IP2

How to understand this clause marked red?

"RF-to-LO leakage in the downconverters refers to the fact that if a signal leaks from the RF to the LO port of the downconverters, it multiplies with itself inside the downconverters. This creates some second-order distortion that cannot be separated from the distortion caused by device nonlinearity."

It means that the IF contains the results of squaring the RF input signal. You will get a double frequency and a demodulated version of the signal in the IF. If you do not do a good job of filtering the RF input certain signals will end up at the IF frequency and pass through your system.

It is very uncommon for this disclaimer to appear so I suspect that this system is especially sensitive to this problem.

I can give one example as an explanation:

If input RF is from 1 to 3GHz, LO is 0.5GHz fixed, for a low-side down conversion case, output IF range will be: 0.5 to 2.5GHz. Compare the undesired 2*RF-LO vs. desired RF-LO, some 2*RF-LO falls into the usable IF band. For example: for input RF signal from 1 to 1.5GHz, undesired 2*RF-LO will be from 2*1GHz-0.5=1.5GHz to 2*1.5-0.5=2.5GHz. They are in-band and cannot be easily filtered.

I think that is what it means. Same analysis applies for up-conversion.