No, its defined to a series of specifications. [0] Ones that define an underlying structure, in bits.
You have a 16byte random string. Thats great. But it is not a UUID.
[0] https://www.rfc-editor.org/rfc/rfc9562.html
> The UUID format is 16 octets (128 bits) in size; the variant bits in conjunction with the version bits described in the next sections determine finer structure.