Yes, inconsistent in that you "detect dampness" beneath the river-bed (you can assume the 'floor' of that water-tile is impervious and not waterlogged, despite the dampness-detection) but an aquifer tile is wet for the whole rocky volume, including the "
floor slice", so digging below exposes you to the water in the wet upper.
It is more logical with detecting magma (you can feel heat through that layer, and also sideways through walls, without expectation of 'seeping', though if you overstep the mark and (wrongly) ignore the warming-warning you've got a potentially larger issue on your hands, and feet.
The worst case scenario (not sure how common to encounter a boundary in just the right/wrong spot) is if you have an actual aquifer inhabiting the layer immediately passing under a clump of water (river, pond, pool, ocean) and you dig into it
knowing that the warning+cancel was just the liquid tile (from checking what you can see of that), expecting a sufficient floor/ceiling separation from actual-wetness, but then discover the rock-seep exists and have to deal with the consequences of that.
(I've only made this error long ago, when there were just normal aquifers, no weaker ones. But in either case the seepage would probably be less than if I had breached the actual river involved, with its gravity
and (for a river) continuing feed.)
Mis-puncturing a static pool of liquid is probably not as bad, and I've deliberately done that for tapping cavern-water, albeit with prepared diagonals and ready-to-reshut floodgates to moderate the flow immediately after breakthrough. If in doubt, prepare? If you've already dug a two-tile-wide (or more) corridor up until the danger-zone, build a mini chequerboard of 'temporary' walls in the lead-up to allow miner access/exit as you test the front but if/when the water starts the diagonals rob enough of the power of the flow to put in an emergency wall (back where there is orthagonal access to do so, also should stop the builder from walling themselves on the 'wet side') and learn from the experience.
Although even if you get
that wrong, perhaps because I explained it badly, you still learn from your experience.