Looks like contact_the_calculator beat me to what I going to say. That's a visual bug; but I've got more input.
Look at the values among his stats and you'll see that he doesn't have the stats he should have if he had two of the given item. Two improved spirit armors, without any other source of spirit armor, would put someone at 69.75% spirit resist, not 53% which his stats show (which show the correct numbers). Beyond that Infernus also has escalating exposure which adds another 15% spirit resist. That pocket only has 15% bullet resist which is the value a single point blank gives, the visual you have there is that he has two.
Yeah he might've felt invincible, that's because you didn't build what you needed to deal with his build and were extremely under-farmed by comparison to him. With that build he had nearly 98% spirit lifesteal and 35% bullet lifesteal, dang right that's near invincible unless you build right against that. Regarding his spirit resistance, with crippling headshot and mystic vulnerability you would reduce his spirit resistance by 43% and his bullet resistance by 24% so long as you dealt 1 headshot in the last 4 seconds and spirit damage in the last 6, compared to the reduction to his resist with only mystic vulnerability which you have, you would be dealing 46% more spirit damage and 24% more bullet damage; without even considering the stat boosts that crippling headshot gives. Combine a 65% heal cut from toxic bullets with the damage increase and he would've been much easier to kill.