You’re quite right, the example given doesn’t have bad row estimates, and other cells are highlighted in red/orange/yellow for different reasons (proportion of time taken, in the case shown).
For an intro to this that goes through several examples, I highly recommend a conference talk[1] by Josh Berkus in 2015/16 that he gave a few times. It has aged pretty well and I’ve not yet seen the basics covered better.
EXPLAIN ANALYZE would have shown you referential integrity (RI) triggers taking most of the time, but it’s still a bit of a leap to work out that it’s due to missing foreign key indexes if you don’t already know
For an intro to this that goes through several examples, I highly recommend a conference talk[1] by Josh Berkus in 2015/16 that he gave a few times. It has aged pretty well and I’ve not yet seen the basics covered better.
[1]: https://youtu.be/mCwwFAl1pBU