Presumably, a broken BGP advertisement. These days, they create breathless "news" stories like this one. Back in the '90s, when small-town ISPs managed to accidentally advertise short paths to huge chunks of the Internet, they broke the whole Internet. It's hard to get too wound up about it.

If you're worried that China is going to MITM your SSL sessions, remove their certificate from your cert store.

If I was a Chinese supercyberspy, I probably wouldn't do something as blatant as routing the entire Internet to China just to get traffic I wanted. I think I'd do something much more akin to spearphishing an overseas Google employee to get onto their internal network.

What the article describes can absolutely be done. Well, sort of. China can't advertise its routes as the "fastest", because internet routing cares little about performance[1], but they can otherwise work to make them an attractive option. It's certainly plausible that they could have pulled in 15% of global traffic.

It's not plausible that they could have pulled in any traffic they so choose, but (depending on where their border is placed) they could have grabbed most of it. Also, it's not necessarily obvious to a casual observer what they could have grabbed.

[1] Internet routing in practice is based mostly on politics, a little bit on cost, and basically just uses performance as a tie-breaker.