At the very least that seems to mean the pin is being toggled 4x on the AtTiny for every 1 time its toggled on the Arduino. How that translates into higher quality audio, I'm not sure.
I probably shouldn't be posting to this thread, already having shown my cluelessness, but my understanding is the greater the sample rate, the greater the "horizontal" resolution if you were to look at the wave form on an oscilloscope.
The vertical or Y (amplitude) is any one of 255 steps (8-bit resolution), which makes for a stair-step effect and the audio quality suffers compared to 10-, 12-, or 16-bit which allows more and smaller steps: more and smaller steps gets you get a "smoother" and closer-to-a-true-sine waveform. Increasing the sample rate in the horizontal or X (frequency) axis is another way to reduce stairsteps and increase quality.
The standard Arduino Atmega chips have a 16-bit PWM ability that the ATTiny lacks. Even if the Arduino's sample rate is slower, the increased vertical resolution may make up for it. I.e., whether it's better to have 8-bit + high sample rate, or 16-bit + low sample rate, is a question I leave to the audiophiles.
Of course, your source sample rate has to match what you output. If you simply output at four times the frequency, your sounds effects will play in 1/4th the time and be and be much higher pitched.