First of all, and very obviously, the show-effect

But secondly:
With 3 smaller turbo's your turbo's rev quicker, resulting in a higher boost at lower rpm.
The 3 turbo's combined, deliver enough flow to feed the engine in the higher revs.
And that all turbo's spit in one manifold is no unsual bussines, look at line engines equipped with 2 turbo's, the majority uses 1 manifold.

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