This sounds perfectly normal due to minor manufacturing differences over time. I know of at least 3 slightly different versions all of which I am certain are genuine product (all direct from Apple).
- Original Series 3 cable with 1 metre cable and all-plastic white puck (with watch, from Apple retail store)
- 2 metre cable with shiny chrome back to the puck (came from Apple retail store, probably 2 years ago)
- 1 metre cable, brushed metallic back to the puck, USB-C plug (Came with Series 7, Apple online order)
I also know there was a very short cable version which I have never seen in real life, and I have no reason to think these were the only variants. All the watch charging cables are safe to use with any version of Apple Watch, but if you have a Series 7 you will only get the fast charge function with the new USB-C version.