I would have a problem with a manager if they did this "publicly" within the team/company. Airing it out on twitter is even more egregious. "Severe incompetence" is somehow understating it IMO, although i can't think of a better description.
If what they said is true:
1) Management hired a developer
2) Paid him for years
3) Gained millions of users
4) Became bankrupt
5) Publicly named the developer as a slacker and the reason the business is failing.
More comments from the founder. Nowhere does he take any responsibility for this mess, just blame blame blame.
"The salary amount isn't unreasonable or excessive. It's the lack of material output that makes it unjustified."
- So, don't pay him for years while bankrupting your project?
"I'm being explicit now since vague tweeting allegations isn't productive."
- Explicitly tweeting allegations isn't productive either. It just makes you and your project look bad. There's no way I'm donating to you now.
"The reason there's no money is because someone took a $130k annual salary and didn't actually work on the project."
- And was allowed to do so for a long time. Also, that's only one part of the equation, was this developer also responsible for fundraising? Or other spending?
"I raised this in March when I looked into it and noticed that for the first two months of the year he had left only two brief comments and created no comments."
- You didn't notice your employees had shipped nothing for two months? Or you were OK with this at the time and are now retroactively blaming them?