That’s cause he makes it sound natural. Not all metrically strict like too many classically trained musicians do. The tempo needs to serve the music not go against it. Yes there needs to be a consistency but there’s room for rubato even in the baroque era
I have the "Celebrated Scarlatti Recordings" made by Horowitz in 1964, and it's interesting to contrast: this is more Romantic, with more rubato and more pedal. Both show off his technical perfection and touch. His pianissimo shadings are remarkable (especially noticeable in K531 and K87).
