Until it's been subject to peer review, it can only be considered a first draft. As has been pointed out, the article seems to ignore more mundane explanations (like CO2 dissolved in water); what it needs to do is rule them out.
Extraordinary claims demand extraordinary proof
Well, in this case the authors of the PDF are describing what other researchers did in the face of anomalous results. It is not the current authors that have ruled out mundane explanations. It is the primary researchers that have no explanation. The problem is extremely evident by what the original researchers did to rid themselves of this strange result. They could neither get rid of the anomaly nor could they explain it.
The position the authors take in the face of these conflicts is that this 14C, which should not be present according to their framework, represents ‘contamination’ for which they currently have no explanation.