When my brain interpreted 'they' singular to refer to a unspecified so-far unnamed person or an already mentioned group, it was definitely confusing to have it suddenly used to refer to someone who had just been referred to by name. This was definitely a novel use of 'they' for me at the time and I don't understand why no-one else ever seems to have this kind of confusion. I did get used to it but I don't think it's as universal as some of y'all realise.

Edit: I just learnt the term 'indeterminate antecedent' from the Wikipedia article someone else linked. Thanks to them, I just got a little bit smarter. ;-)