Thief Build
With 2 incinerator’s I’ll bet fully WvW geared . Power/Toughness/Vitality + Food + Divinity rune.
I’ll garner you’re not 80 and equipped at all? Not really a surprise then.
My guess is Valkyrie gear mix with the trait that gives you 100 crit chance from stealth. With this set up in WvWvW, you can go with a lot less precision and still crit hard with backstab and have more health to soak blows. These builds typically run 0/30/30/10/0 or 10/30/30/0/0 trait wise, which gives them more survivability as well. I actually run a variant of this myself on my thief.
If it’s not that, then my other guess would be that the thief had protection boon up some how. Either from boon stripping traits or rune procs.
Or just a gear gap, like the above post says.