I would say that there is no conflict between the definitions.
An index has (normally) hot, warm and cold buckets. The maxTotalDataSizeMB parameter controls the combined size for all these buckets together. When size limit has been reached, the oldest cold bucket is rolled to frozen (and is no longer counted - regardless of whether this means deletion or archival).
If you have archived your frozen buckets, and need to restore some of them (thawing) at some later point in time, their restored size is not counted towards the maxTotalDataSizeMB value. This makes quite good sense, since thawing 10 buckets would otherwise result in 10 cold buckets being frozen, automatically.