Concat or HKDF? The RFC and COSE-JAVA disagree

[cyberphone]

This is Jim's reference code:
https://github.com/cose-wg/COSE-JAVA/blob/master/src/main/java/COSE/AlgorithmID.java#L54
https://github.com/cose-wg/COSE-JAVA/blob/master/src/main/java/COSE/Recipient.java#L258

This is the IANA registry line for the same algorithm (ECDH-ES+A256KW):
CDH-ES + A256KW -31 ECDH ES w/ Concat KDF and AES Key Wrap w/ 256-bit key

And this is the RFC:
| ECDH-ES + | -31 | HKDF - | yes | A256KW | ECDH ES w/ |
| A256KW | | SHA-256 | | | Concat KDF |
| | | | | | and AES Key |
| | | | | | Wrap w/ |
| | | | | | 256-bit key |

?

Being a developer, I tend to stick to code so I vote for HKDF as the "truth" :)

Thanx,
Anders