Hi Ixixly,
I don't believe it was a sideslip as it immediately made a 90 degree turn to the left.
Also, they landed in the opposite direction of their direction of travel just before the 'wing stall'
I may be wrong. Would love to talk to them and discuss what they did.
I only got my pilot certificate on 22 December 2012 and this event put so many things into 'perspective' by viewing it from the ground.
Cheerio