Would someone explain to a scrub what "route leaking" is? Would this be an issue because the leak receiver could inspect traffic that it wouldn't have gotten otherwise?
A prefix can be connected to several ISPs, and thus be advertised multiple times from multiple places. Each ISP resolves all the advertisements and computes paths to each prefix, sending traffic towards the shortest path received.
The protocol that conducts this process, BGP4, is unauthenticated and managed by a combination of fiddly filtering configurations (often based on regular expressions) and trust. An ISP can advertise any prefix and stand a chance of getting some other ISPs to route that prefix towards them.
Here, what appears to have happened was that a Dutch ISP advertised a bunch of prefixes incorrectly (they may have been advertised in such a way as to make them unattractive options for routing, as a safeguard, but that proved ineffective). China Telecom picked them up and propagated them, and, in doing so, made itself an attractive path for the prefixes for many other ISPs.
Yes, this would allow China Telecom to inspect traffic mistakenly routed to them, though it's extraordinarily unlikely that anything like that occurred.
† ISPs themselves have their own short numeric addresses, called ASNs.
The fact that it's China Telecom speaks volumes to this being a suspected route hijack. It's possible it was just an error on the Swiss colo companies part but somehow I doubt that.