No, you should be able to import the key. Note that there is a copy stored on the slf4j.org web-site which you can download without going through a key server.

The keys.openpgp.org server has an implicit  notion of verified email addresses which I was not aware of.  I am not sure the  key with the FINGER_PRINT=475F3B8... had a confirmed email address on keys.openpgp.org. This may be the culprit.