I've been struggling to find the word for this. Irrespective of whether the person actually deserves it or not, important factor being he thinks he doesn't deserve something he got or got praised for.
That the speaker doesn't believe it can make them excessively humble or overly modest.
It's difficult to capture the emphasis on the speaker's belief in a word or two, but it should be obvious from the context.
I accepted the praise even though I knew I didn’t deserve it. [...] am I guilty of accepting undeserved admiration.
Or unwarranted, unjustified, unmerited, unworthy (credit @InterstellarProbe).
Or inappropriate, disproportionate, excessive.
But this says nothing about whose perspective this opinion comes from (or whether it is accurate).