Njalla states in their terms that the domain is registered under their name. Domains registered under NS6 are in fact registered under your name, not NS6. Therefor making you the owner of them. Since that's how ICANN rules work.

"We register and manage domain names on your behalf through Dynadot, an ICANN-accredited registrar."

means we are acting as a registration service or reseller. In practice:

Dynadot is the ICANN-accredited registrar. NS6 is facilitating the registration and managing it for you. You are the registrant if your name (or your company) is listed in the registrant contact information.

Namecheap for example, started this way instead of using dynadot, used enom, https://forumweb.hosting/14401-is-namecheap-com-an-enom-rese...

or in short; Yes.