I think that's an overly charitable reading.

Whether they "earned" them is disputable — the offer letter specifies one vesting schedule (25% every year), the "cover sheet" from the options agreement specifies other (25% every _quarter_).

So — the OP got the shares he was promised in the original offer letter; but later discovered that some of the documents he later got implied that the vesting schedule should be accelerated compared to what he agreed to.

I think that is probably the funniest way possible to earn a billion dollars; but whether he's "owed" that money/shares, is... up for a debate.