I believe it's AC. It's old and it looks like it's just a spiral
strip.

There is no code requirement to do anything with the interior bonding strip but
most electricians will wrap it around the outside of the armor and clamp it
under the connectror.
The real function of the strip is to bleed off high frequency transients and
the leading edge of a fault since the spiral armor tends to act like a choke.
The strip "shorts out" the loops.