A comment further up said they used Optically Stimulated Luminescence to date the sediment that tuned in to rock. You can read about the dating technique [here](https://www.baylor.edu/geosciences/index.php?id=955929#:~:text=Optically%20stimulated%20luminescence%20(OSL). The rock and the footprint must be the same age as the footprint was made while the sediment was still soft. It was then rapidly covered by more sediment, preserving the impression. Over hundreds of thousands of years, the sediment solidified under the pressure of the overlaying material.

(Edit: fixed link)

Scientism isn't a thing. It's a term / idea invented by YEC as a rebuttal to the statement that "faith is not a path to truth". A sort of "I know you are but what am I?". Materialism or Naturalism may be more accurate way of describing people who believe naturalistic evidence as described via scientific methods - even if they personally do not fully understand the methods used.