This is the place where I got many of the two and three tube Miller F40 fixtures.  There were at least 100 remaining 2 lamp F40 GE fixtures mainly in the basement portion of the place.  Such a shame to see that history gone, but some of it lives on (many with their original ballasts) in my shop.
https://www.youtube.com/watch?v=h7ydXfsY4sU
And a news video of it
http://www.fox10phoenix.com/story/29069829/large-fire-at-abandoned-athens-mill

How did the fire start? It's such a shame to see all that down the drain.

There can be many ignition sources in abandoned places, some just "waiting to happen", even if electricity is disconnected. But i'd guess more towards arson by squatters

Most likely arson, as this place has sat vacant since the early 1980s.  It was in pretty rough shape.  These "urban explorers" went into it in 2011, almost a decade after I got the lights out of it.  2:08 to 5:06 is the building that burned last Thursday.  Notice all the lights still remaining at the time of this video... 
https://www.youtube.com/watch?v=wPiiBv5liyw

Looking at that last video, I don't think I would have risked walking across that floor to save those fixtures. The basement ones are another story...I would have grabbed those if I could have gotten up to them.

This video offers a better look at the damage the following day. It reminds me of a mill right here in Anderson that burned down several years ago (see here). The brick shell is still standing but I've never taken a look inside. Not sure if that one had any fluorescent fixtures.

That is an awesome video!  It was done by a local jewelry store that is located in the strip mall where they launched that drone from.  From their video, I can tell you where the specific lights came from.  The main building that burned is where I got the two lamp General Electric industrials from.  I have some of those in my shop, to the right rear (right of the stage). The building to its right that also burned is where the more rusty two and three tube Miller fixtures came from. To the right of it (in front of the new pole barn) there were a few salvageable various two tube lights like the one you got that has the ballast mounted on top.  Behind and to the back of the pole barn, there were hundreds of lights, mostly the two tube Miller units.  These structures were mostly two story.  We rescued many of the lights just before the pole barn was built as a facility for reclaiming the massive amounts of lumber from those buildings behind, beside and below it.  The structure below that and the one closest to the river did not have any lights or nothing interesting at the time.  The remains of the old boiler house is also below the burned building.  The whole facility was full of asbestos wrapped pipes.  Between my friend Jason and I, we salvaged well over 100 lights from this place, mostly with permission.  Unfortunately, nearly as many were destroyed by collapsing structures, the folks reclaiming the lumber and then the fire.

And that is a HELL of a fire in that Anderson mill! Yikes! Such a shame.  I bet it did contain vintage lighting also.  When did it burn and what caused that?  When was that facility vacated?

I don't know much about the Anderson mill fire except that it was maybe 8 years ago.

Also, check this out...lots of fluorescent fixtures here too but I'm pretty sure they're RS.

Yessir!  I have been in that place too.  It was a part of Thomas Textile.  It has almost totally fallen in now.  The lights were all 2x40 rapid start and a few 2x96 IS Slimline.

Here's a news article showing the pic of the aftermath. Click on the pic to enlarge, can you see what's on the left through the second story window?

http://onlineathens.com/local-news/2015-05-15/athens-firefighters-monitor-destroyed-vacant-mill-cause-remains-undetermined

Good eye, Silverliner!  I bet there aint nothin but a hull remaining on that light though.  They were VERY well hung with galvanized pipe and threaded fittings and were a BOOGER to get down.  It is a shame we were unable to save them all.  Most of the ones in the basement section were all still preheat with their original ballasts and integral tube/starter sockets.