Whether or not he choses to tell you about it or not has no effect on his solidity. In any case, there are plenty of us with solid and public lineages that are calling it "Aiki", so what's the problem?
You can define "strong" any way you like. But for me a "strong lineage" would be authentic, verifiable, and credible. If it's not fit for public discussion then it is what it is, but it's not strong.