Biting / odd behavior?

My husband and I adopted a dog about two months ago. He's about 4 years old, and the shelter told us that he's a Jindo x Shiba Inu mix, though I'm a little skeptical of this because he'a larger than either of those dogs typically get (at least, according to a quick google) and he has a somewhat unique look.

The behavior we're wondering about is this: nearly every time my husband sits down on the couch or gets into bed, our dog will nip at his leg. He ususally just bites the air next to his leg without actually touching, though once he did touch with teeth lightly.

I was worried it might be resource guarding or something of that sort, but he'll only do it exactly once when my husband first sits down, and then he'll hop right up and cuddle like nothing happened. He also only does it to my husband, never to me.

I'm just wondering what he might be trying to communicate when he does this and whether this is a behavior that we should be concerned about. If it is, how would we go about training him to stop? I appreciate any thoughts or insight!