Cleverness can be defined as innovation, which means doing something people have not done before you. In that case, the poet has done something clever when he took a road no one else had, or that few people had. It may not be that no one has taken the road, but just that fewer people have.
Then took the other, as just as fair,
And having perhaps the better claim,
Because it was grassy and wanted wear;
Though as for that the passing there
Had worn them really about the same …
To extend the metaphor, because this is what the poem is really about, it is brave to take risks, and can also be interpreted as clever. It depends on what you do once you take the road. Just the act of taking the road is not much. It is an initial choice to do something different. It is what you do that is different that matters.
We can interpret the speaker’s words in the last stanza of the poem to mean that when he took this less-traveled road and did something different from everyone else, he was happy with his choice.
I shall be telling this with a sigh
Somewhere ages and ages hence:
Two roads diverged in a wood, and I—
I took the one less traveled by,
And that has made all the difference.
Of course “all the difference” is open to interpretation. I guess if you are a pessimist you could say that it could be a bad difference instead of a good difference. However, given the context of the poem it seems like the speaker took a different road and is happy with his choice, so it was a good difference for him. Whatever decision he made and innovation he decided on, it worked out and he had a successful and happy life after all of it.