At first glance, I think this could be a reasonable NC, unless you can show otherwise. E.g., "there is only 1 oil type available on the premise to fill these containers and the person(s) responsible for filling them can therefore only fill from that 1 drum/nozzle/etc." It would seem to depend on the criticality of that specific oil to the process, and the potential for "wrong oil" to be used. (Indeed, since it is not labeled, the container could be used to hold coffee, varnish, paint, hand soap, etc.!)
TS9002:2016 8.5.1g doesn't really help much here, as it simply states "g) the organization should take actions to prevent human error such as..." There is no qualifier. However, for 8.5.1 overall, it does state "The organization should consider the full cycle of production and service provision when determining what needs to be controlled...", which implies that for sub-clauses a-h it is within the discretion of the organization to make that determination.
So, after all that, if there is no history of nonconforming product or failed machinery/processes related to using "wrong oil", then it would seem this is a contestable NC. At the same time, labeling containers at work stations on the floor seems to me a good practice, with low cost/effort to implement and maintain, even if the risk is considered low.
So, if this was the only NC I could see accepting it. But since there is a pattern of overreach by the CB, then I can see why you appealed it.