While it doesn’t matter what direction non-polarized capacitors are soldered into a circuit, some feature a stripe indicating which contact is connected to the outer shell of the capacitor. The article describes how to best take advantage of this in your designs.
The outside foil of a spiral-wrapped film capacitor shields the inner conductor. In a simple low-pass R-C circuit, figure 1a, one side of the capacitor is grounded so it makes good sense to connect the striped end to ground to shield the signal side from electrostatically coupled interference.
What about the high-pass case, figure 1b? Neither side of the capacitor is grounded. But generally, the previous stage driving this circuit (perhaps the output of an op amp) is a low impedance that would be less susceptible to induced noise. So connect the stripe to the low-Z side.