All idiots lights On

I have a fully loaded outback, nav, xm, yes,
full auto. It happened on thanksgiving day
when all my idiot lights came on first thing in
the morning when I started the car. I turned it
off and then I turned it back on, same thing. I
needed to make a few errands around town,
(drug store, grocery store, and gas station).
The last stop was a gas station when I got
out of the car, a rat came out from
underneath my car! I filled up and left the
station. By this time, the idiot lights remained
on the whole time while the car was running
and nevered went off, except when the car is
off. I suspected that rat was underneath the
hood since I left the garage. And found
evidence of rat dropping on the engine and
behind the engine with some insulation and
exposed wires! I think the rat sabotage the
system in my car. I took it to the dealer under
my insurance, and the dealer did their
inspection and replaced the insulation and
checked out the system. They told me that
there was no wires eaten by the rat and that
the gas cap wasn’t sealed off correctly and
that was the cause of all the idiot lights being
on! So The the question is; does a loose gas
cap can cause a the idiot lights to go on?! I
thought it would be only the check engine
light  only, not all the other lights! If that
were so, why didn’t it come on before that
day before my next fill up?! Can someone tell
me is that possible for all the warning lights
to come on for a loose gas cap?!