That is correct littlespider. Your Account level is just the sum of your Hero Levels therefore your Account always levels when your Hero does and you only receive one Loot Chest when leveling up a Hero.
For Bestial, I looked into the issue you reported here where leveling Sylvanas to level 10 only granted you one Chest. On my testing accounts and my personal account, when I hit a level 10 Milestone, I saw one Common Loot Chest and one Hero Loot Chest, as well as the bonus gold. This caused my Loot Chest pop up to say I got 3, when I correctly got 2. If you level another Hero to 10 and look at your Loot menu afterwards and do not see the Hero Chest and 1 additional Loot Chest, please take a screenshot and show me here!
Thanks!
Huginncord