Duping is where you duplicate items, it's a glitch exploit and requires no 3rd party programs/clients etc.
There were no bridges to any side islands in the map. I watched you play for about 3 and a half minutes, and relogged your inventory frequently to see if anything updated.
Here was your inventory on diamond items, I excluded your iron items- yet you did have 500 iron ingots worth of porkchops alone, not counting the other iron items in your inventory.
I apologize in advance for this essay of a reply.

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(2x) Iron Sword (20 diamonds) (TOTAL: 40 diamonds)
(1x) Diamond Pickaxe (20 diamonds) (TOTAL: 20 diamonds)
(2x) Bow (14 – 28 diamonds) (TOTAL: 28 - 56 diamonds)
- The bow that you were using did not have the max enchantment: fire aspect, so the bow types you have had ranged from 14 - 28 diamonds)
(66x) Bread (8 bread = 5 diamonds) (TOTAL: 40 diamonds)
(6x) Golden Apple (1 golden apple = 15 diamonds) (TOTAL: 90 diamonds)
(4x) Obsidian (4 obsidian = 4 diamonds) (TOTAL: 4 diamonds)
26 Leftover diamonds (TOTAL: 26 diamonds)
(66x) Arrow (2 arrows = 2 diamonds) (66 diamonds)
Chainmail chestplate (12 diamonds) (TOTAL: 12 diamonds)
Iron Helmet (10 diamonds) (TOTAL: 10 diamonds)
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Your inventory is worth about 364 diamonds.
On the map you were in there are three middle diamond generators.
Two level three generators, and one level four generator.
Every 20 seconds a level three generator gives 2 diamonds, and every 20 seconds a level 4 generator gives 3 diamonds. So every 20 seconds the middle generators produces 7 diamonds.
I question if your claims are true.
If your inventory is worth about 364 diamonds, and your match lasted 20.5 minutes then that would mean you- all by yourself- despite enemy players- and despite your own teammates collecting from those at well, it would require you to singlehandedly collect from all the diamond generators in the middle for 17 minutes out of the 20.5 minute match.
And if that wasn't enough I refreshed my log multiple times while you stood in the middle for a few seconds and watched 5 golden apples appear in your inventory when you were no where near a shop.