The Honda, like the Renault, uses a turbo smaller than that of the Mercedes, one which can more easily compensate for the thinner air by spinning faster to further compress the thinner air. At its lower homologated burst point speed, the Mercedes turbo is not quite compensating fully for that 25 per cent reduction in air density.
Is the burst speed homologated? I've seen nothing in the regs to that effect. Max speed is defined in the regs and likely measured real time by the SCU, but there is nothing stating the PU manufacturer has to prove anything other than, when in use, the turbo rpm does not exceed 120k rpm.
Sounds journo BS to me.