But the rest of those have nothing to do with their legal team. They wouldn't implement a copy of another OS into this OS without making sure it was legal to do so.
Ozweiller is quite right. Big companies copy other people's stuff, breach trademarks (Metro?) and generally mess up all the time.
I doubt the ABI emulation is actually a problem, but calling it "Windows Subsystem for Linux" might well be a trademark violation as it doesn't involve Linux itself. Imaging if Wine called itself "Linux Subsystem for Windows". I think Microsoft would be deploying their legal team right quick.
It might not have been simple to do, but still - hard not to see the outcome.
The very fact that they had to pull the plug seems to suggest that it was not desired, and as such, it should have been safe guarded against.
An example safeguard being, limit what it can say. If it has racist/etc stuff in it, literally don't send to twitter. The bot still learns, the algos don't change, and Microsoft still gets to see what the given AI will behave like in full public. And above all else, the bot isn't a Microsoft branded Hail Hitler AI.
It sounds like you believe what happened is perfectly within reason - if that's the case, why do you believe they pulled the plug?
All in all, this is a lesson that some high-profile person/group eventually had to learn on our behalf. Now, when an unknowing manager asks why your chat bot needs to avoid certain offensive phrases because, "our clientele aren't a bunch of racists", you can just point him to this story. The actual racists are tame by comparison to what trolls will do to your software.
[0] = https://github.com/shutterstock/List-of-Dirty-Naughty-Obscen...
However the legal department of every company on the planet makes a risk:benefit analysis, especially in fuzzy areas like copyright law (which we've seen with the Java case....an API isn't copyrightable, then it is, then it isn't, then it is). The assumption that if Microsoft did it therefore it must be without risk is folly.