Odd Wedding Invite?

My boyfriend works for a small business where everyone is friends. One of his coworkers was getting married and we received only an Evite that said wedding and ceremony at 6pm. We showed up at 6pm to realize the ceremony already happened at 4pm and that the reception started at 6pm… The invitation didn’t say anything about that being the order of events or that we were only invited to the reception. After talking to our friends at this reception we realized we were the only ones (other than one guy that we know of) whose invite said 6pm. Is that normal? What is the protocol on only wanting certain people at the ceremony? It was quite embarrassing once we started talking about it with all our friends. We felt left out and confused as to why we weren’t considered as close to him as some other people who admitted they hardly knew the couple. We also chose an expensive gift off their registry based on the assumption they invited us to the most important part of the wedding which is the ceremony. Also, we never received a thank you card for the gift. Am I being sensitive or is any of this rude?