This means that a person named Piotr Jastrzebski created a commit in February. This is a different commit based on that one (not in the sense of revision ancestry, but in the sense of rewrite history): this commit is the N-th rewrite of Piotr's Jasterbski's commit, for some N > 0, and the rewriter ("committer") is Narayan Kamath.

The rewrite can have different content: for instance, it can be altered to merge against a different parent.

An example of a rewrite is a simple cherry-pick (e.g. from one branch to another).

All these things are commits. The initial authoring is a commit, and this latest rewrite by a different person is a commit.