I don't think you'd sound disingenuous by simply stating things as you've done here: You had no idea you'd get such a strong response and can't possibly handle that many testers at one time. Clearly, hundreds of beta testers mean that you'l have to spend hundreds of hours responding to their requests. You'll never get out of beta. It's better for everyone if you get a product they can use to them faster.

I don't think anyone will deny you the right to make a living based on the fact that you said something overly specific in the past.