He did not make any distinction between Himself and God in the first place! Rather the contrary is true:
The Lord affirms clearly that there are good men who take out of good storage of their hearts good things, and bad men, who take from their hearts bad things (as more often than not we all witness) (Luke 6:45).
Is the Lord, humanly speaking, any worse than those “good men” He mentions to exist? Stupid even to suppose so! Thus, if somebody can be called “good” humanly speaking, then the Lord is the first in their elite list, for goodness of men is estimated by their good actions, and the Lord's good actions are second to nobody with regard of empathy, justice or courage.
But then why did not He accept from the youth this appellation? Just because the youth saw in Him only a human dimension and in human dimension every good man is such not per se, but through participation in God's grace, which is per se good and is an uncreated and inseparable aspect of Him who is per se good and provider of grace that goodens the participant.
Now, the Lord reprimanded the youth for not acknowledging in Him the Good per se, the divinity, and in order to underscore this point, He even intimated to the youth that He is not only Perfect, but also the perfection-provider to all who would follow Him ("if you want to be perfect, leave everything and follow Me" /Matthew 19:21/), and the perfection-provider must necessarily be essentially or per se perfect, and such is only God.