Read the manual of your washer. I’m willing to bet it instructs you to run the tap until it’s hot before you start the dishwasher. This is common for American dishwashers, because they can’t get the water hot enough, fast enough, for the prewash cycle

In the video he mentions that the machines heat for a set time and not for a target temperature. So as majority of machines (in US market) are meant for hot water input. Then if you feed cold water they don't heat it enough

depends very much on where you are, unfortunately. in USA, this is definitely not the case, they're almost all incredibly dumb. especially the cheapest-possible models that most renters are forced to use (and renters account for about a third of all households).

as a concrete example, the video has a section in it where he shows that his doesn't so any sensing - hot or cold water have exactly the same timing on the heater's use (and resulting water temperature graphs).

so like. I agree with you that it should be true, it's simple and cheap to implement and it obviously works better. unfortunately it's not a sane reality for tens (hundreds?) of millions of people.