Clarification of the OP:
Going back to our previous thread, there are two aspects of the overall timestream: Length (Growth of Branches) and Depth (Number of Space-Time Layers).
In the comic, Ben states that there are millions of space-time dimensions that are like Ben's, Rex's, and the Null Void.
Holiday would say that there are theoretically infinite space-time dimensions that are like Ben's, Rex's, and the Null Void.
With Paradox and Ben 10K, they are discussing the branches and how they keep going ad infinitum (Latin, literally ‘to infinity'). Maltruant goes on to say that the overall timestream is infinite. With infinite length, the growth of branches is infinite as well. These two support the 'infinite' tweet since the universes refer to the branches.