I think, IOW, that keys contains the equivalent of #'(a b c) (assuming the invocation was something like (hash.refs table a b c)). When putting this list in, without a quote, it would expand to (hash-refs table (a b c) #f). This is unlikely to be correct; what we really want is (hash.refs table '(a b c) #f).
With syntax-parse this kind of example is a bit clearer, but Fear of Macros does a nice job connecting the dots between low-level macro primitives and higher-level DSLs like syntax-case/syntax-parse.