The CatalogManager checks for CatalogTableImpl instead of CatalogTable to decide whether to resolve the table schema. See https://github.com/apache/flink/blob/release-1.11/flink-table/flink-table-api-java/src/main/java/org/apache/flink/table/catalog/CatalogManager.java#L369
Resolving the table schema adjusts the type of fields which are referenced by watermarks, i.e., changes their type from TIMESTAMP(3) to TIMESTAMP(3) ROWTIME. If table schema is not properly resolved some queries involving time attributes will fail during type validation.
However, CatalogTableImpl is an internal implementation of the public CatalogTable interface. Hence, external Catalog implementations will not work with CatalogTableImpl but rather CatalogTable and hence might fail to work correctly with queries that involve event-time attributes.