[chockchocschoir]

Another non-confrontational way of dealing with this issue is to engage the first time they do it, and when the conversation is about to end, tell them "hey by the way, in the future I'd appreciate it if instead of saying "hey" and waiting for me to reply, you'd just write me the question in one go, as that would be less distraction for me. Thank you, hope you understand" or something similar.

This way there won't be any misunderstandings about why some people seem more responsive than others, because now that person knows how to communicate with you.