"If sampled sounds are used for an electronic piano, then the inharmonicity of the low strings as recorded would contain frequencies that would beat unpleasantly with the high notes - stretch tuning would therefore be used."

If you start with 'sampled sound', there are 2 ways to go

1) EACH NOTE pitch is sampled individually, stored and played back - uncommon.

2) Far more common, especially in the early days of 'sampling instruments' was to just sample ONE PITCH, then 'play it faster or slower' (sorta like 'dopplering' it) to generate the other pitches. This unfortunately often gives a false impression of what a real instrument may sound like.