They can, and they do. You can see that in your history because you can listen to the audio of things it decided subsequently was not intended for it.
But unless you have multiple devices, those make up a relatively small proportion of requests, and hence most of the time false positives is something they have a strong incentive to stop because it causes negative user experiences.
[If you have multiple devices it will happen "all the time" when a request is genuinely meant for a Alexa device but more than one device hears the request, but then it has no UI effect - one device will usually answer, and the other(s) will stand down; this is by no means perfect, but it works reasonably well]