He is most certainly confused and has a flawed understanding of Bitcoin. I can't seem to recall something in my thought process so I thought I'd ask. We know that blocks bigger than 1 MB from chain B would surely get orphaned on chain A. However, what about blocks from chain A being relayed to chain B (considering this would be a 'unilateral split')? I don't see why 1 MB blocks from chain A would get orphaned on chain B under current conditions. Care to elaborate?
This is where an unilateral split gets tricky, and why BU needs majority hash rate.
Let us say that block A1 is the last common block ( A's are less than 1MB). BU pulls the trigger at that moment. What does that mean ? They mine at least ONE B block, bigger than 1 MB: B1.
We now have: for BU nodes: A1 - B1
However, for old nodes: only A1 (B1 is invalid).
BU has more hash rate. It now builds a B2.
For BU nodes: A1 - B1 - B2
for old nodes: A1 (both other blocks are invalid).
Now, a "minority miner" mines A2, built on top of A1 (B1 and B2 are invalid blocks for him).
For BU nodes: 2 chains: A1 - B1 - B2 OR: A1 - A2. First chain has more PoW ("is longer"), so winning chain: A1 - B1 - B2
for old nodes: A1 - A2 (other blocks are invalid)
As BU *has more hash rate* this will continue.
At no point, an "A" miner will build upon the B chain (invalid blocks), and at every point, the BU nodes will see more PoW in the B chain.
But, but, but, drama and catastrophy. If BU now becomes minority hash.
We have:
A1 - B1 - B2 - B3 - B4 ..... B250
A1 - A2 ..... - A100
For a while, everything goes still well. But A having more hash rate, it will grow faster.
So after a while, we have:
A1 - B1 - B2 ..... B500
A1 - A2 ..... A-501
BOING!!!
Now, for the BU miners, the A chain is the longest. They will add their new block to the A chain:
A1 - ... A-501 - B502
But for the (majority hash rate) A miners, this is an invalid block.
They will also mine an A502 block.
And then an A503 one on top of that. B502 gets orphaned.
Next, the BU miners still find:
A1.... A501-A502-A503 a valid and longest chain.
They will add B504 on top of it...
But the A miners will outcompete them with A504 and A505. B504 gets orphaned....
And the B chain is dead.
Everything that happened on the B chain is as if it never happened.
Unless the B miners decide to implement something that makes it a bilateral split. A soft fork on B is thinkable, that A doesn't have.