a proper diff of the issue:

diff --git a/lib/dns/cache.c b/lib/dns/cache.c
index 10e2331..4f234e2 100644
--- a/lib/dns/cache.c
+++ b/lib/dns/cache.c
@@ -1581,7 +1581,7 @@ dns_cache_renderjson(dns_cache_t *cache, json_object *cstats) {
 
        obj = json_object_new_int64(isc_mem_maxinuse(cache->mctx));
        CHECKMEM(obj);
-       json_object_object_add(cstats, "HeapMemMax", obj);
+       json_object_object_add(cstats, "TreeMemMax", obj);
 
        obj = json_object_new_int64(isc_mem_total(cache->hmctx));
        CHECKMEM(obj);