Sounds like a plausible scenario to me, there's definitely an incentive to ruin the largest cryptocurrency to promote regulation.
Even with 51% they'd have enough if they are creating a separate chain altogether instead of competing for every block.
They easily could have stockpiled enough equipment or older gear that was taken out of use to get the additional single digit % needed.

Although as a counterargument, one would expect the decline in hashrate would have happened much faster if it was coordinated.