Why do tombstones exist in the scylla_cdc_log table?

Installation details
#ScyllaDB version: 5.4.10
#Cluster size: 6
os (RHEL/CentOS/Ubuntu/AWS AMI): CentOS
Hi !
After I turned on cdc for the table, I found tombstones when scanning the cdc_log table. The log is as follows:

querier - Read 0 live rows and 1163 tombstones for alternator_test.test_scylla_cdc_log partition key \"fe32969696969767612f582002e21\" {{-129875865724610921, 0010fe32969696969767612f582002e21}} (see tombstone_warn_threshold)",

Isn’t the cdc_log table only for writes? Why do tombstones exist? Is it related to TTL?

Yes it is related to TTL. Expired cells are identical to dead cells (tombstones) in the internal representation and are reported as such when calculating this tombstone statistic during read.