The other people at your table were rude. You are allowed to wander around and visit people at other tables before the meal is served, and after the meal is over. But during the meal, you sit at your assigned table and eat with the people there.
This applies to you as well. You could have gotten up before or after the meal was served and gone over to one of the other tables and asked, "Are you all Groom's friends? I'm Dragon Heart; I'm friends with Groom from work/school/childhood. I've been wanted to meet you guys; I've heard so much about you." But you didn't have to do this. (I'm very shy, so doing something like this would be very difficult for me, but for some people it seems easy.)
But for four people to get up and leave one person stranded at a table? Even if I'd have been rude enough to change my seat, I'd have seen that one person sitting there and felt badly about it and moved my chair back to that table for the meal, at least.
Guests have obligations to the host, just as the host has obligations to the guest. The host has to provide adequate food and drink for the time of day, and see to the guests' comfort--enough chairs and tables, etc. This is what is known as hospitality.
The guest also has obligations. This is what is known as comity, an atmosphere of social harmony, or mutual courtesy and civility. A guest is supposed to dress appropriately, arrive on time, use their best behavior, fall in graciously with the host's plans, and when seated next to someone they don't know, introduce themselves and carry on a conversation for the time that they are sitting down. It's all part of being a polite guest, just as much as thanking your host at the end of the party is.
You did a great job under the circumstances. I'd have been tempted to rat out the groom's friends as being totally without manners, but you were able to refrain.
The other guests were rude to you, to abandon you at the table like that. They were rude to the host, to not follow the seating chart. They were rude to the waitstaff, because the serving of the tables was now messed up.