[benwad]

In the 00s there was a popular wine called "old git". It generally means someone grumpy and cantankerous, but in a playful way (otherwise you'd just call them a c***). So it makes sense for a self-effacing joke about Linus Torvalds.

[xanderlewis]

This is true. But I think there’s a surprising difference between calling someone ‘an old git’ / ‘a jammy git’ / ‘a grumpy git’ / … and simply calling them ‘a git’. The latter seems quite a lot harsher and less likely to be a joke.