Your regex concat command creates a regex that looks like:

  (foo|bar|baz|)
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That trailing "|" allows an empty match.

This is why all elements matched.

Try removing the trailing "|". This is the canonical way to match a bunch of different things. Also, you do not need the parens, unless you are capturing.

Lastly, use a "join" instead of looping and concatenating - that will also avoid the trailing "|".