90% pretty certainly means they were selling them at a loss, but I would agree that it's probably not as huge a loss as a 90% discount would suggest. In the "enthusiast" branch of the market, I would guess that a margin of at least 50% should be pretty standard. A $250 mouse very certainly costs far less than $250 to produce, although you always have to factor in their other business cost - advertisement and design to establish an "enthusiast" branch might even exceed what they pay on manufacturing. (This is also why you see them do so many sponsorships - it's simply a very, very cheap way to get exposure.)

I would think that it's not impossible that this was planned.

1234 as a coupon code is even something that people might find by mistake, meaning you wouldn't even have to try hard to seed the rumor. Just put it into the system and know that somewhere in the future, you will get a huge PR without much effort (other than stopping it after a certain period of time and accepting some losses).