That IEM is an extreme in impedance values that will magnify other impedance variations and also challenge the amp section with a near short circuit condition at some frequencies. So if your plug is higher impedance than the other, it might change the FR audibly, or even on occasion change how loud you need to go to make some amps distort.
@theveterans suggesting that IEM makes sense IMO, as if something is going to sound different for impedance related matters, it's more likely to happen on that IEM. It's not a typical case, it's clearly a hyper extreme. It doesn't validate anything for the average IEM either. But when seeking audibility of impedance variations, it's the killer sample of IEMs.