While it is true that what is unbounded in all respects is indefinite, that which is unbounded in just one respect is not. There would be nothing indefinite about a rod that just went on and on in one direction. The argument conflating the infinite and the indefinite is fallacious. The argument goes that what exists must exist in some quantity, but may exist in any quantity. The concept existence is formed by omitting measurements of entities, which again must exist in some but may exist in any quantity.
Finite quantity is a redundancy.
Infinite quantity is a contradiction in terms. Though we might only be able to grasp and measure what is finite, that we be able to grasp and measure X should never be taken as a criterion for X existing. To demand that nature should conform to such a degree to human powers of cognition errs also by the fallacy of the primacy of consciousness. The concept infinite cannot be made as a concept of an actuality. But it can be one of potentiality.