I think you have enabled "Show system objects" option from Preferences dialog due to which you are able to see them in types.
Could you confirm that by navigating "File" -> "Preferences" -> "Browser" -> "Display" (Check screenshot for more information), If it is set to "True" then this not a bug and it is expected behaviour, You can set it to "False" and reload pgAdmin4 if you don't want to display system objects.
OS Windows 7. Postgres 9.6.5 PGAdmin Version 2.1 - Python Version 2.7.13 - Flask Version 0.12.2 - Application Mode Desktop
When viewing my DB through PGAdmin, it shows I have 233 types. It seems that PGAdmin is displaying every sequence and table as a type. The create type command in the SQL window has the tableoid, cmax, xmax, cmin, xmin and ctid columns as well as table column names. The sequence create type command shows the same system columns as well as all of the properties of a sequence.
None of those types show when I execute \dT from psql or when I view types within PGAdmin 3.