Where do these suggested contacts "from my adress book" come from? I recently bought a Google Nexus 10 and created a new Google profile (@gmail.com) associated to it. I never sent any email from it neither received anything except Google's welcome messages.

I added two personal IMAP accounts (full of emails).

Then I installed Twitter (I'm new to Twitter too) which suggested me to add contacts from my "address book", that are actually real people I know.

Does Google look into my IMAP mailboxes to discover my contacts ? If not, how is it possible for it to suggest such friends ?

(My address book is empty - the only existing contact is myself. I also have a Dropbox and Github accounts linked to Android, but these account doesn't store contacts.)

I saw Where exactly does Android get its contact suggestions from? but my GMail address is totally new so nobody has it.
First off, this almost certainly is nothing to do with your new Google account.

The Twitter app has access to all the accounts on your phone with which it can suggest contacts. This means it probably looked at one or both of your personal IMAP accounts and used those to suggest contacts to you, rather than you 'empty' Google account.

The question you linked to is probably correct although instead of your Google email address the suggested contacts probably have one of your personal email accounts in their address book.