I divided China's change in emissions since 2015 by the global change in emissions in 2015.

(12533.4 - 10355.2) / (40812.4 - 37467.3) = 2198.2 / 3345.1 which is... 65.7%, far from 90 percent. If they mistakingly used the graph of CO2 emissions that excludes other greenhouse gasses it still only gives 74.3 percent.

At this point I give up where they pulled that from

Sidenote: doing the same for 2023-2024 gives China a share of just 33 percent of increase in emissions.