[resoluteteeth]

When they say the threshold is zero they mean they haven't identified any specific amount below which there stops being any effect, but the effect is still dose dependent so the effect from incidental consumption is negligible and undetectable (except maybe statistically if there are large populations that are identical except for consuming or not consuming then).

This is in the context of debate over whether some harmful things like radiation or ingestion of heavy metals go linearly to zero or of there is a specific threshold below which they suddenly stop being harmful.

It doesn't mean that all quantities of alcohol are equally harmful.