As others have pointed out, cones such as these merely attest to volatiles in the subsurface. CO2 is harder to keep in the shallow subsurface unless it's frozen, but this area is too near to the equator.

OTOH, If you have a large-scale mobilisation of sediment that is saturated with liquid CO2 - i.e. a "mud", then when it stops, the excess CO@ will boil out through cracks and spouts, building Phreatic-like cones that were produced without heat.

Isidis Basin (target of Beagle 2) contains many thousands of such cones.

My take on cones

If that thing makes it there it may detect mineralogical evidence inconsistent with magmatic processes and consistent with CO2 solution.

or then again the evidence may be inconclusive as so often on Mars!