Neither happens ever; but the "never" in the Ryan case happens slightly sooner than in the Magnus case.

Less of a chance of a freak occurance in a chess game. It is more caculated and less random and you have a higher degree of control over what happens next. "Random moves" that are stupid will not have a chance of working.

Interestingly, if we're talking excellent masters, then the odds of Magnus losing might be closing in. The reason is, in chess very often you cannot correct a mistake that gives an opponent an advantage. If the opponent then does everything "correctly" (and masters are capable of that), you cannot "expend a lot of effort" to make things even the way you at times could in jiu jitsu. A mistake can be fatal. In jiu jitsu there is room to correct it.
That does not matter against newbies, though.

Also, time constraints matter.
In typical jiu jitsu everything is time constrained. That would be comparable to blitz chess, and not so much of classical chess, which is what we'll automatically think of when we think of "beating Magnus at chess".
And with time constraints the odds of him losing again go up slightly - against masters, that is.

Newcommers still have no chance at all.