The reloading HDB part is as if "\l ." is run by HDB. This step for a partitioned database, among other things, loads serialized objects of the current directory (e.g. sym file) and caches things like splayed tables in the latest partition. It is necessary to make HDB pick up changes introduced by an external process, e.g. a new symbol may be introduced while saving the tables.
The relevant doc is https://code.kx.com/q/basics/syscmds/#l-load-file-or-directory
