What blocks a query in Postgres
That your query on the lock table didn't return anything provided the answer to your question--it was not waiting on a lock.  (Assuming you did it correctly).

It is still kind of annoying and error-prone to have to open a new session and run the query and interpret the results, so I wrote a patch to send NOTICE when you are waiting on a lock.  There were several proposed ways to improve it, but no consensus on the best way, so for now it is just a proposal.  If you are willing to compile your own PostgreSQL you can always adopt this patch for your use.  I don't know what pgAdmin will do with such notifications, however, as I use psql not pgAdmin as my main tool.

As @a_horse_with_no_name indicates, you can also use columns in pg_stat_activity to get information on this.  The quality of that information improves from version to version.  Running older versions does come at a price.  Putting in the effort to upgrade every couple years is well worth it.

Finally, your system monitoring tools are invaluable. A quick look at "top" (for Linux) or "Task Manager" (for Windows) would probably have immediately indicated that your job was busy doing something--either CPU or disk.