When it first rolled out the office install actually adds a teams installer rather than teams itself (and no choice to avoid it). So then teams would reinstall with every restart after being uninstalled and pop up front and center asking you to sign in every time windows started.

You then needed to sign in before it would give you the option not to start with windows or to only start in the background.

Obviously you could avoid this by uninstalling teams and ALSO it's auto installer. I'll add the caveat this may have only been the behaviour for those with skype for businesses installed or those in NZ(I've heard NZ is occasionally used as an early roll out/testing zone for some microsoft products) rather than more generally.

This was an accident. It took a bit to remedy but that was not the intention.

I don't use MS Office, 365 or otherwise, but my understanding is that there wasn't an option to set it to not install teams on initial install.