X11 "bleeds" the output of programs to the tty

I use bspwm with a simple .xinitrc config file instead of a display manager, and there is only a simple exec dbus-launch bspwm command there. Whenever I start a program via, for example, dmenu_run (which itself is started via sxhkd after sourcing bspwmrc file), the output from that program goes straight to the tty from which the X session was started. For instance if I run echo it will write the message to the tty, instead of just ignoring it (despite the fact that, from my understanding, there shouldn't be any file descriptors to which echo could write). What confuses me most, is that many other programs that can too write to stdout (steam, firefox, mpv...), actually don't pollute the tty despite also being started via dmenu_run. **Why?** And the worst thing yet, some programs like w3m, not only show their output but also stay interactive even after exiting the X11 session. **Why and how** does this happen, and how can I prevent it?