DBCC CloneDatabase - sys.partitions rows value wrong
If you intend to use the cloned database for production use, specify the VERIFY_CLONEDB option which also clears the statistics in the cloned database.

VERIFY_CLONEDB
Verifies the consistency of the new database. This option is required
if the cloned database is intended for production use. Enabling
VERIFY_CLONEDB also disables statistics and query store collection,
thus it is equivalent to running WITH VERIFY_CLONEDB, NO_STATISTICS,
NO_QUERYSTORE. This option is available starting with SQL Server 2014
(12.x) SP3, SQL Server 2016 (13.x) SP2, and SQL Server 2017 (14.x)
CU8.

https://docs.microsoft.com/en-us/sql/t-sql/database-console-commands/dbcc-clonedatabase-transact-sql?view=sql-server-ver15
This is an artifact of the history of this command.  Initially it was just for troubleshooting, but was later enhanced to enable you to use the cloned database for production.