I have no doubt it is honest, but it's not a good apology. He barely remembers the specific incident (by his own admission). That's not his fault, but it makes the apology pretty much meaningless. He seems to assume he was a bit of a grumpy-puss that day, and that "jaded" their subsequent interactions. This is incredibly glib and diminishes the specific incident.

But more importantly, he never admits to being a bully. The original post gives this incident as an example of a pattern of abusive behavior. He sidesteps that entirely.