first of all, if you think you are right, why not use your real github account, then discuss publicly what is your problem with disposable emails? (there are some problems definitely, but it really depends on how company is going to handle that issues, that's another topic)
it really feels you are trying to offend them by creating new github account and making commit to fight against Hey email.
secondly, he is a co-founder of company, so he is trying in anyway to keep their email reputation, why he should not? some companies might be fetching that lists automatically every week and marking as a spam every email coming from that providers, which hurts company.
regarding, disposable emails, I do think they might be used for spam or other purposes, but there could be a ways to prevent these issues, why not give a chance to company? maybe they will setup limits for disposable emails, you can create 100 for read-only (for signing up in some phishing web-sites), 10 for sending emails up to 10 per month? they will figure out. But as a community we should give them a chance.
Just show your public face, make open public discussion, so that people will decide at the end.