Holdsworth,

[Milkfloat]

Maybe the chainring was starting to wear and rather than flip the chainring the owner decided to flip the whole lot.

 

[raleighnut]

Lokks like a fixed/free set up but instead of flipping the hub they flipped the crank, easy with a cottered crank

 

[Hover Fly]

Is the stem expander bolt missing? Might indicate a seized stem?

Yes it is missing, I haven't checked if it'll move, tomorrow maybe.

This might be silly, but I can’t see much detail on this tiny screen, but it’s not a head-clip is it?

 

[rogerzilla]

Left-hand drive BMX kit is available because some riders prefer to grind using the RH pegs.

 

[Sharky]

Could it be that the culprit screwed the freewheel onto the hub the wrong way and realized that you only had traction when back pedaling. He would also realised that the removal notches were on the inside, so no easy way of removing the freewheel.

So he then moved everything to the left side to overcome the issue.

 

[T4tomo]

more likely to be a double fixed hub isn't it, given complete absence of brake? And then at some point someone has decided to run the chain down the LHS.

 

[Illaveago]

I wonder if they used a crank from a tandem ?
Wouldn't the sprocket on the rear wheel loosen if used in the opposite direction ?

 

[rogerzilla]

Some people run LH fixies just to be different. The lockring prevents the sprocket unscrewing and the pedals are ok if fitted with threadlock.

 

[Mark Grant]

Is the stem expander bolt missing? Might indicate a seized stem?

Stem was indeed seized. It took quite alot of effort and penetrating oil to get it out!
The good news is that the frame & forks have matching numbers.