Compactor calls getCompactionCompressionType() and uses it during compaction:
this.compactionCompression = (this.store.getColumnFamilyDescriptor() == null) ?
Compression.Algorithm.NONE : this.store.getColumnFamilyDescriptor().getCompactionCompressionType();
While getCompressionType() is used by the flusher - see code in DefaultStoreFlusher#flushSnapshot():
writer = store.createWriterInTmp(cellsCount,
store.getColumnFamilyDescriptor().getCompressionType(), false, true,
snapshot.isTagsPresent(), false);