I love geeky discussions like this Tuning is a complicated mess. While we use mathematics in an attempt to explain and describe tuning practices, our ears fight against that, which is what causes the problems. Another significant problem has to do with equal temperament, which was developed, I believe, to solve the problems with tuning keyboard instruments and fretted string instruments in which each pitch must be fixed. Such a tuning scheme is simply a compromise that essentially allows such instruments to play relatively well in all 12 major and 12 minor keys in Western music.
HOWEVER (don’t you just love “howevers?” - LOL), instruments that do not have very rigidly fixed pitches - essentially, orchestral string instruments, woodwinds, and brass. Yes, even woodwinds have a fair amount of room to bend pitches up and down - although the oboe is used tune the orchestra because its pitch has the least amount of room for variance - pitch on the oboe is mostly locked in by the reed. Anyway, orchestras and other groups do NOT use equal temperament (GASP! Oh the horror of it all!!!)! LOL! For example, our ears tend to like thirds, sixths, and leading tones to be slightly high when playing in Major keys - because they sound “better” to our ears. What this means is that the “same” note will have a slightly different tuning that is dependent on the key! GASP! LOL. As an example, in C Major, A is the sixth and will be played just a little high and will be slightly out of tune with the piano (or other fixed-pitched instruments). However, in F Major, A is the third and will be played in tune with the piano (or other fixed-pitched instruments). So, does this mean that orchestras play out of tune when performing, let’s say a piano concerto? YES! GASP! Why? Again, the orchestra sounds better and a very slightly out of tune keyboard (on a few notes) isn’t noticeable to most people. It’s all a compromise.
BTW, a similar situation occurs with music using minor scales although non-fixed-pitched instruments will play the third SLIGHTLY flat - it helps emphasize the feel of minor keys.
One interesting (informal) discussion of this may be found here:Tuning
Finally, I think that the guy on the first video wasn’t necessarily saying that mathematics was driving pitch up, per se, but that our ears hear certain intervals, a certain way in relation to other intervals and that this eventually leads to a change in key, because of how we hear them. (Does that make sense? I’m thinking out loud now.)