From what I can tell, that's more or less what happened and what introduced the vulnerability, someone could make an illicit site called something like illicitx.com, and post it as illicittwitter.com. Basically they feed on real/safe websites that had Twitter in their name, and make an illicit version with x instead and the change would redirect them to the illicit version
actually url/uri spec is surprisingly complex, I'm not even sure it's possible to fully/correctly match it with regex without false positives or negatives, especially in twitters case where even things like "google.com" are accepted as valid urls (without the protocol part, which is otherwise mandatory)