Distributed algorithm can be executed in a single process
From Wiki:


  Distributed algorithms are a sub-type of parallel algorithm, typically executed concurrently, with separate parts of the algorithm being run simultaneously on independent processors, and having limited information about what the other parts of the algorithm are doing.


It is inherent type of algorithm to be run independently with no requirement that processors are in the same machine. Think of it as the type of workload being cut into independent pieces.

From Wiki:


  A distributed system is a network that consists of autonomous computers that are connected using a distribution middleware. They help in sharing different resources and capabilities to provide users with a single and integrated coherent network.


So the algorithm is distributed, but the system you have described is not. This is just algorithm with different purpose run in less distributed environment with potential to be sub-optimal in such setting.

Another example: you can run sorting network (say bitonic sort) in one thread, it doesn't make it serial algorithm, but overhead is costly in such case.