I think "legitimate interest" has a different meaning in the context of GDPR. I'm fairly certain about this, but you don't need to take my word for it: https://duckduckgo.com/?q=gdpr+%22legitimate+interest%22&t=h...
As I said: if your interpretation was correct (in this context) it would be a loophole so big it would make the rule meaningless.
> The difference is that they now have to inform you that they are doing it...
I don't think so. AFAIK the difference is they now need to make it opt in and voluntary.