Is the code open source? How would one know with certainty their data isn't being surreptitiously copied?

(You can also recreate this functionality locally with a few lines of Python):

import pandas as pd

import os

list_of_files = [f for f in os.listdir('.') if os.path.isfile(f) and ".csv" in f]

print(f"Files that will be concatenated are: {list_of_files}")

original_df = pd.DataFrame()

for file in list_of_files:

  df = pd.read_csv(file, keep_default_na=False)
 
  original_df = pd.concat([original_df, df], axis=0, ignore_index=True)

original_df.to_csv(f"Output file.csv", index=False)