I'm playing with the MQTT broker at 'broker.emqx.io' and have subscribed clients to the topic '/python/mqtt', which is the default topic in a Github repository containing an example client implementation in Python. My subscribing client is receiving messages published by my publishing client in the example code. In the time I've spent running the code while modifying it apparently no other client in the entire world has published a message to the topic. Is there something magical going on whereby subscribers in my local network receive only messages published from my local network? Or is there just no traffic on the topic?
The simplest answer is the most likely, there just isn't anybody else running that example code at the same time against the same broker.