The mistake is being attributed to a human email sender as perceived by the email recipient, not to an AI, since it's an email suggestion. Many such email senders will know the recipient's gender better than the AI, and the recipient will know that.

As for your broader doubt that misgendering leads to offense, that's a longer conversation than I can shoehorn into this thread today, but the Geek Feminism wiki is one of several good places to which you can turn to start learning about that topic if you want to.

I'm a cisgender man myself, but I have heard enough personal stories from friends who aren't to know that misgendering can and often does offend.