A couple of implausibilities. For one, I'm not ready simply to believe that one EGR valve example came from a vehicle running for 30-something thousand miles with 37 (IIRC) cetane fuel when a few moments later he states that the lowest that you can find in pump Diesel in the US is 40 (ASTM D975).
His description of the Diesel combustion process also elicited guffaws, rolling eyes and face palms. Diesel combustion does not burn "well down into the power stroke" as has already been discussed elsewhere here. In fact, both Diesel and gasoline engines have relatively comparable combustion durations. In the industry, combustion duration has a standard definition like the number of crank angle degrees from 10-90% mass fraction of fuel burned (MFB) - therefore mostly ignoring ignition delay - although some use different conventions like 5-95% or what have you, but 10-90% is the most common I've seen to talk in the same language among combustion engineers. Both gasoline and Diesel engines have 10-90%MFB between 30-45 degrees crank angle. In the scheme of the whole power stroke in the worst case, when the crankshaft has rotated 45 degrees out of 180 to go from TDC to BDC, the piston has only descended about 18.8% of the length its stroke (18mm out of a 1.9 TDI's 95.5). Regardless of the precise numbers, the salient point is that the combustion durations of SI gasoline and CI Diesel engines ARE ABOUT IN THE SAME BALLPARK.
Also the statement about gasoline needing octane to "slow" down combustion and Diesel needing cetane to "speed it up" is an incomplete, simpleton explanation at best and moronic at worst. The fact is, "speed" here needs to be clarified. All hydrocarbon fuels burn in the same order of magnitude - certainly within say 20% - of laminar flame velocity; this applies when talking about methane (CH4), propane (C3H8) and complex, heavier liquid mixtures like gasoline, naphtha, kerosene, Diesel and heavy fuel oil.
What a higher octane rating does do for gasoline, is make the fuel air mixture more resistant to spontaneous combustion, particularly in the end-gas ahead of the normally propagating flame front that starts at the spark plug; it is this combustion ahead of the flame front and the collision of multiple fronts at detonative speeds that cause knocking. Octane does this - nothing more and nothing less.
What a higher cetane rating does do for Diesel - which was accurately captured in the lubrizol Youtube video - is that it shortens the delay period from the start of injection to the start of combustion. Cetane does this - nothing more and nothing less. Once combustion starts underway, however, the cetane rating has essentially no effect whatsoever and it's up to other factors such as volatility and fuel-air mixing rate that become the most dominant. Having more or less cetane than optimally designed for a particular engine can have impacts on fuel economy and emissions - but some peer-reviewed studies have shown that while certain emissions may go down, others may actually go up, and those that actually do go up are counter to what most advertisers of cetane boost products claim (namely soot); the effect of too low cetane is most tangibly manifested by higher white smoke (PAH) during cold-start and by louder and "harsher" combustion - longer ignition delay with more time to form a premixed charge and followed by rapid and sudden burning of said premixed charge.
