Is this sentence a meaningless tautology (application code is not the same thing as patents) or are there some older patents that Microsoft isn't donating? For example the VFAT patents?
It's not in the ZDNet article body either, just in the small lede under the header. The body instead says,
> You see, Microsoft, with the major legacy exception of its Windows desktop and desktop application code, is an open-source company.
It seems like an editing mistake or a badly worded statement.
When they donated the IP to OIN, for all intensive purposes the patents were liberated given OIN's wide coverage.
Even if you got a license for a patent for yourself and wrote free software for it, if someone else gets it they might need a patent license too, regardless of your project being free software.
Your FOSS/FLOSS license might include a patent clause but that means you'd first need the right to issue licenses for the patent, in case you don't, the clause is void.