Understanding “max_wal_size” and “min_wal_size” parameters default values from postgresql.conf file

According to documentation, for "min_wal_size" and "max_wal_size" parameters
<https://www.postgresql.org/docs/9.5/static/runtime-config-wal.html&gt;

default values are:

For max_wal_size: The default is 1 GB

For min_wal_size: The default is 80 MB

Then I look this parameters from my database config:

select name, setting, unit from pg_settings where name in
('min_wal_size', 'max_wal_size')

Gives result:

name | setting | unit----------------------------------
max_wal_size | 64 |
min_wal_size | 5 |

I have 2 questions:

1) Why these values doesn't match default values, which are shown in docs?
I never changed config settings at all.

2) Why unit column is empty/NULL for these parameters? What means 64 and 5
values in this case? MB? GB? or what?

Why this is not like for example work_mem parameter, when everything is
clear:

name | setting | unit----------------------------------
work_mem | 4096 | kB