This is true in only the strictest sense, as computers only deal with integers:

Any set of tuples/sequences can be lexicographically radix-sorted if its components can be; strings are a special case, where the components are the individual character codes.

Floating point numbers are integers with the high-order bits used for the exponent. When normalized, they can be treated as integers for sorting.

All radix sort requires is a recursively partitionable domain, and it performs optimally when the partitioning scheme matches the data distribution.