There are different implementations, and BCD is only one of them. Another popular one is a mantissa and exponent, but the exponent is for a 10-based shift rather than the typical floating point.
Tbey mean radix-10 floating point, as compared to the radix-2 floating point you are thinking of. The packing of the decimal fractional digits in the significand of a radix-10 FP number need not be in BCD, it can use other encodings (e.g., DPD or something else).
0.3 is exactly representable in radix-10 floating point but not radix-2 FP (would be rounded to a maximum of 0.5 ulp error as seen in the title), for instance, just as 1/3 = 0.3333... is exactly representable in radix-3 floating point but neither radix-2 or radix-10 FP, etc.
