Like others have mentioned this definitely sounds like the last of a long chain of emails.
And it really has the tone of just because you do it on your own time, with your own personal email as a “hobby” doesn’t mean you can use it as a loophole to get around restrictions IBM employees might have.
So, for example, if IBM isn’t allowed to contribute to a specific project for legal or contractual reasons, an employee doing so “in their own time” would not be a defensible argument.
It still has ramifications for personal contributions on their own time. We are our own persons, with our own desires and choices not to be dictated by our employers. I work for a corporation that says they own every piece of executable code that comes out of my fingertips and I think it is utter bullshit.
If I want to fix a bug in an esoteric Scheme implementation OR a bug in a JDK or PHP I have to ask for permission even though it is on my own time. I already volunteer more time than I am paid to my employer, but I have to ask for permission for something they have literally no interest in.
I agree that these things tend to overreach (the more powerful party in a negotiation will always try to get as much as they can), but most employment agreements will only claim ownership over things that you do in your own time that are related to your company's line of business. And in states like California and I believe Washington, companies cannot legally try to claim more than that. It's still more than I'd like, but I also can't get too worked up about it.
One way around that is to never put your real name on stuff outside of/owned by your employer. Keep your work and personal life as separated as possible.
Trying to do an end-run around legal issues by using pseudonyms is something you should only do after careful consideration of what might happen if that pseudonym becomes known.
It's not unreasonable to review and modify the proposed contract that an employer offers.
As skilled employees who's services are in demand, you've got a good chance of them coming to the table on that.
And it really has the tone of just because you do it on your own time, with your own personal email as a “hobby” doesn’t mean you can use it as a loophole to get around restrictions IBM employees might have.
So, for example, if IBM isn’t allowed to contribute to a specific project for legal or contractual reasons, an employee doing so “in their own time” would not be a defensible argument.