Yes, it does that because it was designed to sound convincing, and that is a good method for accomplishing that. That is the primary goal behind the design of all chatbots, and what the Turing Test was intended to gauge. Anyone who makes a chatbot wants it to sound good first and foremost.
This happens sometimes in my own writing when I'm revising quickly. Of course I don't have an editor and I'm just commenting on Lemmy and Reddit, but same idea. First I write it using one phrase, then I revise it to another phrase while leaving behind a trace of the removed phrase. The final sentence might check out grammatically but not logically, so a simple grammar checker could miss it.