EXPLAIN ANALYZE does not return accurate execution times

[Mark Mizzi <mizzimark2001@xxxxxxxxx>]

As an example, let's take the following simple table:

CREATE TABLE unary(a VARCHAR);

-- simple way to make table large
ALTER TABLE unary
    ALTER COLUMN a SET STORAGE EXTERNAL;

-- insert one million large rows
INSERT INTO unary
SELECT repeat('a', 8000)
FROM generate_series(0, 100000);

-- update planner statistics on the unary table.
ANALYZE unary;

When I run

EXPLAIN ANALYZE SELECT * FROM unary;

I get the following result:

 Seq Scan on unary  (cost=0.00..1637.01 rows=100001 width=18) (actual
time=0.009..6.667 rows=100001 loops=1)
 Planning Time: 0.105 ms
 Execution Time: 8.565 ms

On the other hand, the following command

time sudo -u postgres psql -c "SELECT * FROM unary" -o /dev/null

returns after 17s with:

sudo -u postgres psql -c "SELECT * FROM unary" -o /dev/null  0.01s user
0.01s system 0% cpu 16.912 total

I am running Postgres 14 (installed via apt) on Ubuntu 22.04. All settings
are default.
The machine is a Dell Vostro 7500.

All commands are being run locally, so I don't think this is a network
bandwidth issue. What's going on?