Hey Kevin,
You raise a great question and several important points. I would caution labeling emotional neglect when seeing only one isolated incident. As you mentioned the parent could have been having a bad day and wasn't able to respond to the child in that moment. There's also the possibility that their experiences haven't provided them with parenting examples or supports. Whatever the case may be, in this situation I think leaning towards relationship building instead of resources giving could be an option. Your engagement with the little girl is a great example of this. I'm wondering how the parent would have responded if they were engaged. Maybe start with a statement: "Looks like your kiddo took a tumble!" Open the door for the parent to respond and possibly offer more information or start a conversation. Websites can be great resources, but there is definitely the risk of the parent interpreting your suggestion as "I see you're not a good parent, please visit this website." If the parent is having a bad day, they may welcome the opportunity to vent and if they could use some support as a parent, then you've opened the door for further conversation. You could always look at local parenting groups or classes that could be passed along if the parent is open to it.
Thanks for caring about kids! I hope this gives you some additional insight.
-Laura