Is all email tagged as spam, spam?

Not necessarily. The system is not foolproof and there will be instances where legitimate email is tagged as spam and where spam is not tagged as such. This is why only high scoring spam was tagged as spam, however you can change the setting in your cpanel:
a) login to cPanel
b) click on MailScanner
c) click on Other Settings
d) Change High scoring spam setting from default 10 to lower number for example 7
e) Click Change button to save the setting