What was that all about

I am writing this because I just don't know what to make out of this. Maybe if whoever reads this can help me.

On May 27th, I received an e-mail from a long lost cousin. I was very surprised to say the least. The e-mail was an invitation to attend her oldest sons graduation party. I was very touch that she would even want to extend the invitation. We were never close as children. In the e-mail I was asked to send her my other brother and sisters e-mail addresses so they could get an invitation as well. I thought maybe now that we are adults with our own families she maybe would want to try to reconnect. One can only hope. I accepted the invitation. In her e-mail she never said when the party was going to be. She did say they were watching the weather to pick a date. I replied that I would be happy to attend the party, just let me know what the date would be. I never got a reply. To this day I am still waiting for the date. Then on on May 30th, I got a phone call from my sister who said she never got an invitation and that the party I was invited to was held on Sat. May 29th.
My sister said our brother received a phone call from our Aunt who invited our brother to the party. Our brother did not go to the party. When I heard this I was so mad. Who goes to the trouble of sending a empty invitation? What kind of person does that and WHY?
In other words, What was that all about?