No way. Your chain got worn. Take a link apart and you'll see, or just lay it flat on the table and try pushing/pulling it lengthwise. There'll be play, because the surface of the inside links that is in contact with the pins is worn. The side plates are exactly like new, but the inside links are now loose on the pins.
Too tight chain, bad chainline, dirt, not enough lubrication, low quality chain or high gear mashing accelerate this.
You can call it stretching, terminology doesn't matter much... But physically it is wear.