hole in chain stay

Today there was a guy with a MTB and on the
chain stay there was a small drilled hole,
maybe 5mm in diameter. The hole didn't go out
on the other side so it was just one entry
point. It looked completely undramatic to me
but he insisted it reduced strength. Well, of
course, but not to a degree where the tube
would fail, right? I'd estimate the tube
diameter to 2cm plus change. It was an old MTB,
90s or the Millenium, so does that mean most
likely steel and possibly aluminium? BTW, are
carbon frames like horror story glass-fiber
boats in the sense that a crack thru
micro-vibrations can make steady but all but
undetectable progressions before the whole
thing come crashing down?

--
underground experts united
http://user.it.uu.se/~embe8573