a) it's $100k we didn't have, and which we greatly appreciate. We have a 'donate' button on the site, but that's basically a few dollars a day, more or less. It will pay for pizza for a sprint every few months, and that's about it.
b) we've supported Windows for years, money or not. The core team isn't made of Windows experts, so our support may not be always ideal, but we always test on Windows, have Windows CI running, and always release Windows installers. Windows is widely used and we want the experience there to be as solid as possible. The money was a donation, no strings attached (under US law it can't have strings attached, since it's a donation to a 501c3).
And salaries in academia aren't all that high. I'm one of the lucky people being paid to work on IPython (from another grant), and while I'm not a senior developer, $100k would cover my salary for well over a year.
b) we've supported Windows for years, money or not. The core team isn't made of Windows experts, so our support may not be always ideal, but we always test on Windows, have Windows CI running, and always release Windows installers. Windows is widely used and we want the experience there to be as solid as possible. The money was a donation, no strings attached (under US law it can't have strings attached, since it's a donation to a 501c3).