It's easy to understand he meant 21 millions coins.. 21M bitcoins.
Source: emails between Satoshi itself and nostr:nprofile1qqsy2ga7trfetvd3j65m3jptqw9k39wtq2mg85xz2w542p5dhg06e5qpz4mhxue69uhhyetvv9ujuerpd46hxtnfduhszxrhwden5te0dehhxarj9enx6apwwa5h5tnzd9az7qgwwaehxw309ahx7uewd3hkctczcs834
https://mmalmi.github.io/satoshi/
