Coolant and overheating help?

I just bought a 2002 Chevy Silverado
5.6 liter from my 95 yr old grandfather.
He takes really good care of his
vehicles and the truck is in good shape.
But I think he made a mistake of
putting window washer fluid in the
coolant tank in the past. On my
message board it'll say Low Coolant
every now and again. So I'll have to refill
the coolant. Today I stopped and left
the truck running with the AC on for
several minutes and when I came out
there was antifreeze all over the
parking lot and the engine was
steaming and it smelled like ammonia
inside the cab. (That's how I figured he
made that mistake). It drained almost
all the fluid so I refilled the tank with
new coolant. After running more
errands it again said Low Coolant but
never overheated. Do I possibly have a
clogged hose from the window fluid
being in it for so long? Or is it possibly
a leak? What kind of damage would
that mistake have caused? And what
should I do from here?