A couple years ago I would have been all over this. I've done several ventures similar to this resulting in modest exits as well as couple resulting in being simply paid for working 4-12 weeks on something I want netting nice contacts.
It's okay if you don't hit a home run. It's even better if you don't starve or get evicted for your troubles.
I wouldn't take this deal, because stopping / starting employment isn't that easy for me
But for those people who freelance, and are in between jobs this may well be an ideal opportunity to (continue) being paid for doing something they have been thinking about for a long time.
Just to put this in perspective, I live in a Central European country, part of EU, I earn almost 2x national average and I have to work about 4.5 months to get that kind of money.
$ 8000 is 1-2 months salary for a top developer in Brazil, depending on experience. To work on a side-project you're trying to get off the ground, it's fair.
I assume he was thinking in R$, not dollars, with a slightly <2x exchange rate. Either way, a developer is not going to leave a good paying job like that, if he can just save for a few months and own 100%.