Person who has unfriended me is trying to get in touch

Someone unfriended me over 12 months ago. I created a group 8 years ago. I think that this was just for a get together in 2010. I have not used it since. I no longer have this group in my groups. I think that I deleted it some time ago, but did not delete all the members. I have set my facebook page to only accept friends in all my securiy settings. One of my friends has not deleted this group and neither has the person who unfriended me. The person who unfriended me has apparantly messaged me using this old group. I presume this is because they cannot contact me any other way. Am I right with this assumption or not? I do not give out my phone number and only I can see my phone number in facebook. My friend has seen this, but I cannot see it and do not particularly want to see it. Can my friend see it, just because I did not remove the members before I deleted the group? Will the person who has unfriended me, see that I have not been able to see this? This would be helpful, as I would hate to think that they thought that I was ignoring it.