Evidence is not based only on that! (and I am sure you know that too)
First of all there is evidence that they performed surgical procedure on workers. If they were slaves, do you think they would try to heal them, or just simply replace them? Also they found evidence that workers belonged to groups, and that there was kind of competition between the groups (who will do more).
Also, it's not just fish that they found, but all different kind of food, including bones of animals. By analyzing the worker bones, they figure out that workers have been feed really well. Also they found a whole bread baking village. Another discovery happened after they found workers houses. They lived family lives, which also brings idea of them being a worker, not slave, as it was believed before.
And for the end, there might be some slaves, but it's not as it was believed before, and you have right to have your own opinion, and believe whatever you like. For some reason I found one of professors from British archeology team to be more trustworthy then you.
