Meredith appears to be telling the truth. She didn't say Len wasn't Satoshi, she simply said to the best of her knowledge he wasn't. That doesn't mean he wasn't working on it covertly.
One of Len's best friends (Bram Cohen) knew Len was posting pseudonymously on the cypherpunk mailing list but never knew what handle he was using. Also, when Bram was about to release BitTorrent Len tried to convince him to do it anonymously. It's not hard to believe that Len would have done it secretly; even from his wife.
Furthermore, Meredith can't be 100% trusted. When Satoshi handed the project over to the maintainers and stopped posting to the cypherpunk mailing list in late 2010, Meredith tweeted, "Bitcoin isn't ready for prime time yet, according to its creator. Interested people can help finish it, though!"[1]
Satoshi never said those words publicly or privately-- so it's a curious thing to say.
As for the computer...
It's likely Len used university computer(s) for the development as the commit times and communication line up with an academic schedule. It's likely the university had Windows computers. Plus; it's one way to isolate the environment and reduce the chance of information leakage (could have even been a Windows VM).
[1]: https://twitter.com/maradydd/status/12163582133276672?t=dk8C...