Apple Watch series 7000 compared to series 1

The 7000 is not a series of Watches. It is the grade of aluminum of which some of the first watches were made.

M1 Mac mini, macOS 11.3.1; Watch, series 5 GPS/cellular, watchOS 7.4.1; iPad Pro 2nd Gen, iPadOS 14.5.1; iPad Air 2, iPadOS 14.5.1; iPhone 12 Pro, iOS 14.5.1; TV 4th Gen, tvOS 14.5  HomePods, audioOS 14.5 and Airport Express w/ Airplay 2

It can be the original or the series 1 Watch, both had a series 7000 aluminum alloy version.

Series 7000 aluminum alloy is the strongest alloy of aluminum. It is also used in the aerospace industry.