You not listening. Colilns is considered a LB in PK's defense. He actually drops (see the long the screen TD) and is involved as a SPY. Sorrell drops occasionally also, though much less. We all remember seeing 6'7" Ethan Burke dropping. The numbers only refer to how many DL, LBs, and Secondary players there are. The typical Texas lineup is Simmons/Moore, A Collins, Broughton, and Sorrell. PK characterizes the Buck and Jack as LBs, hence it is a 2-4-5. Though it looks like a 4-2-5.
A 3-3-5 looks like a 4-2-5, soon as you put a LB on the edge. You will see a 3-3-5 that looks like a 5-1-5 with 2 LBs on the edge. You see these looks all the time. When you say 3-3-5 or a 2-4-5 cannot hold up against the run, it is not correct. Lot of DC will use what is characterized as a 3-3-5 or 2-4-5 for the flexibility. You can put 5 or 6 on the LOS and drop 1-2. You can put 4 on the LOS and drop none. I believe when you say 3-3-5, you are speaking strictly of a 3-3-5 stack. Even then lot of those guys will blitz a LB to morph it into a 4-2 at the snap.
PK's 2-4-5 looks like a 4-2-5.
https://www.on3.com/teams/texas-longhorns/news/the-pete-kwiatkowski-defensive-glossary/
https://www.footballstudyhall.com/2015/5/1/8528407/modern-defense-and-the-2-4-5-vs-the-3-3-5\
This why I said dont get caught up how the defense is characterized, unless you want to go down that rabbit hole.