though I sure don't know why it's returning "=28"

That's the bitwise string-OR of the stringified decimal representations of the three values, i.e.

"128" | "8" | "4"
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or, more eplicitly

chr(ord('1') | ord('8') | ord('4')) .    # '='
chr(ord('2') | ord('')  | ord('') ) .    # '2'
chr(ord('8') | ord('')  | ord('') )      # '8'
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