Well picking AM into Razor(static link+eye of the storm vs melees), Viper(viper strike+his orb against melees), Enigma(black hole against melees) and Batrider(lasso) was already a pretty fucking retarded choice. It's no wonder they were surprised cause the pick was fairly dumb, you don't pick a melee carry into this lineup, even a tanky one which AM isn't, he's just gonna have a horrible time. On top of that those 2 carries actually build tanky which makes it harder, for example while Drow or Luna are very good against melees, they're also squishy bitches and if AM blinks on them and abyssal them he can fold them instantly, not so much when the first items the enemy carries build are aghanim into heart or shit like that.
They had a good window of opportunity however to simply outfarm and starve them with prophet split pushing all lanes safely forcing them into the base while AM clears basically everything else on the map(ancient to ancient clearing jungle on the way). Then at 45mins your AM is 6slots, your furion is 6slots, and you force a fight in the base and win it while their carries are outfarmed. Instead they started taking fights, playing sloppy, fed solo kills left and right(not even like 5man smoke type, just herpderp let's try to gank them 3vs5). If you looked at the graphs at the time, I don't think Tobi was showing them but not sure, they fed them SO MUCH XP. Gold not that much but still enough that the gold lead was basically not increasing the entire time, but xp is a big deal when the enemy team is 5manning non stop and staying in the base, that means when you finally push they're vastly underleveled making it easier. Instead in like 10mins they had fed Witch Doctor enough xp to go from lvl 11 to lvl 16, and you definitely don't want to do that because WD's lvl 16 ulti is A LOT stronger than lvl 11 since it adds a bounce to it on top of obviously increasing dmg.
After that it was just a slow death, they fucked up capitalizing on their advantage, ruined it then couldn't fight anymore because the way they had been playing didn't let them win at equal farm, only if they were ahead. If they had farmed WR a lot in the meantime and made better item choices I think they would have stood a chance. They needed a vlad for AM, Furion needed to be full combat(necro fucking sucks at 45+mins, put it on a courier and buy an AC or mjolnir or crit or bkb) and WR needed to have at least 3 strong combat item, preferably sheepstick mkb daedalus. With that I think they can take fights and win, if Rubick steals blackhole.
They just showed how inexperienced they were in lategame while LGD in typical chinese fashion showed they can handle it just fine against a team that's not flat out superior to them.