Completely disagree. I found no problems with the tone here. Instead, you have an insider who shares a few implementation details to give us an idea about the depth at which they go to prevent data loss failures. I saw nothing in his post as "bragging".

The guy lost everything because a temporary team membership was revoked.

What would you like him to do, apologize profusely and robotically without knowing the details of this incident? Dropbox is a decent-sized organization and I am pretty sure they have guys already responsible for addressing specific issues like this. To expect every employee to know details of every issue seems unreasonable.