I think that this is a wrong interpretation. The NAPTR returns only the SIPS service (I used some other router—obviously). The associated SRV lookups return the usual 3 (out of more) edns.t-ipnet.de servers (which can create problems further down the road).
It looks as if only secure connections are now possible regardless of the location of the PBX. Insofar the video could refer to an older setup and you might have to enable TLS/SRTP. You may not be able to enable TLS and use unencrypted media.
It could still be possible that you are not using the associated Telekom DNS server that would allow using unencrypted connections. A PCAP trace would show that. I would assume that Mr. Griebsch would have updated his video in case Telekom would have changed its policy.