In Co-op as a Baroness, wielding a Capital Sniper Rifle (Incendiary), mysteriously got a Deadlift Quick Kill through shields

In Co-op as a Baroness, wielding a 92 damage Capital Sniper Rifle (Incendiary), and 600+ on a crit. Mysteriously got a Deadlift Quick Kill through shields.

While grinding up / carrying my Gladiator, I decided to take on Deadlift solo, because I got everyone to his Bastion of Bounce for the location EXP anyway.

So, as my LV 9 Baroness wielding a Blue-rarity Incendiary Capital Sniper Rifle, where I tried and failed a few times, suddenly mysteriously, I land a hit and Deadlift dies while still at a lot of shields. I think.

Anyone know how that happened? I wouldn't think that him being affected by Cold As Ice would matter?

Unless he can actually freeze and be shattered? But that's just a guess I just made. I've never seen a boss be frozen.

On fighting him again, his Health Bar seems extremely weak compared to his shields, actually. Such that it seems like it only took one hit to bring him down? So it might be just that? But I don't know how much HP he has vs. his shields.

What's the odds that I actually had a glitch vs. I just wasn't paying attention and accidentally drained all his shields then took him down with a headshot?

Or in another manner, "What's the Shield amount and HP of a LV6 Deadlift?"