What Vitor is pointing out here is extremely important, BUT it is very easy to misinterpret it as: "RELAYS ARE TRACKING YOUR NPUB AGAINST EVERY QUERY YOU MAKE"

which is just false, since they can't. They can however see every write that you do. So can everyone else, but they can also associate your IP to it. So use a VPN.

Now what this post is hinting at is that relays CAN do meta analysis to figure out who is querying these posts(by looking at follow lists and author filters) or which IP is browsing what content, so they can create a profile to some degree. Which is why you SHOULD connect to trusted relays.

Just pointing out the hidden details so people don't get the wrong ideas from it.