You don't have to be an expert in TypeScript to know that the TypeScript compiler just strips the types from the code and leaves the rest as-is (if you are targeting a somewhat modern JS engine). The runtime performance of a TypeScript program is the same as that of the equivalent JavaScript program.
But of course, a TypeScript program could be much slower than a different JavaScript program, as is probably happening in this case.
I agree with others that the difference in results between JavaScript and TypeScript makes the quality of this paper highly suspect.
We are talking about the benchmark game here. The code for different languages was written by different programmers. For some languages, there were multiple implementations and many iterations. In this case, the researchers used the fastest one.
Some of the implementations are extremely optimized and took a lot of effort. Some implementations are not. So you might be comparing highly optimized JavaScript code with naive, below-average TypeScript code. You cannot compare those.
It would be much better if they used the same level of optimization for each language, but they didn't. Furthermore it is called a "Game" (it used to be called a "Shoot-out") because you shouldn't take it seriously. So it shouldn't be the basis of serious research.
I think this is quite a serious issue which has been open for almost a year. I don't understand why there hasn't been a reaction from the npm developers on the issue (as far as I can see). npm 8.3.1 (the current version) is still vulnerable.
It might not be directly exploitable but it can leave you open for all kinds of security and/or stability issues. It is also a regression from npm 6.
But of course, a TypeScript program could be much slower than a different JavaScript program, as is probably happening in this case.
I agree with others that the difference in results between JavaScript and TypeScript makes the quality of this paper highly suspect.