Assigned seating is not always the case... And, often isn't necessary.
I would never presume to tell every guests where they would be placed, and who they would sit next to!!!
Adequate seating, IMHO, would be mandatory.
I am really questioning the situation, because, I would imagine that any reputable venue would be contracted to provide food and drink for a fairly specific head count.
Of course, I was not there, and have absolutely no idea... But I do suspect that the person(s) who planned this reception way under-reported the estimated guests, in order to cut costs and to try get out of paying.
Funny, back in the stone ages... I had a small family and close friends wedding and reception. It was a fairly simple buffet luncheon.
We had been honest with the number of people expected.
Some witch woman working there actually tried to come up and ask us to pay for another punch-bowl, as it was running low!!!!
Lovely thing to do to a bride...
I hadn't planned for coffee, at a luncheon.
Ends up my DH's family are coffee drinkers... I found out later that DH's uncle slipped one staff member some money and requested that they set up a pot of coffee!!!