"if I didn't, millions would've died" - mixed conditional or informal english?

This is the conversation between Peter Parker and Assistant vice chancellor in the Spiderman: No Way Home movie

Peter Parker: Yeah, I'm sorry. I really needed to talk to you and I know you're on your way to the airport. MJ Watson and Ned Leeds are the two smartest people I've met, and I'm the dumbest person because I let them help me, but if I didn't, millions would've died, so please don't let MIT be dumb like me.

Assistant vice chancellor: MIT is dumb?

Peter Parker: No, I'm saying don't let MIT be dumb. I mean, like the dumber version of me that wouldn't have let them help.

Assistant vice chancellor: You didn't rehearse that, did you, Peter?

The context is: Peter did let MJ and Ned help him. Because of that, millions didn't die. He's talking about a past event.

When I used AI, and asked why “If I didn't... “is used instead of “If I hadn't...”, it replied

This is because spoken English often relaxes grammar. Native speakers frequently use past simple where formal grammar expects past perfect, especially in fast, emotional speech. Examples: Formal: If I'd known, I'd have called you. Casual speech: If I knew, I'd have called you. Native speakers say this all the time.

IS THIS TRUE ??

It looks like wrong usage of mixed conditional !!

There are plenty of similar examples in the TV corpus. Apparently in oral English, it's not all that uncommon. A sample below, and there are many more.

If I didn't make it back alive, she'd have kicked my arse. And now she just has to wipe it. (The Royals; The Counterfeit Presentment of Two Brothers; 2017)

You did this? You paid my bail? Why? Judge set the bail at the max: $2 million. If I didn't do this for you, you would have been looking at a year before you even got a trial. (Touch; Accused; 2013)

Are you buying me? Is this the way you get girls to go out with you? I'm still here. You're taking this wrong. If I didn't leave you that tip you wouldn't have come, we wouldn't have this argument and there wouldn't be this heat between us. (Friends; The One with the Hypnosis Tape; 1997)

Oh, my God. I must be crazy. What have I done? -Oh, no. What's wrong? -What's wrong? I'll tell you what's wrong. I just committed adultery. You didn't commit adultery. I did. Oh, yeah. If I didn't do it with you, I would have done it someone else. (Seinfeld; The Good Samaritan; 1992)

There is a note in the conditionals section of A Comprehensive Grammar of the English Language on this construction.

In informal AmE the hypothetical past is sometimes used for past reference in place of the hypothetical past perfective:

If they invited her to the conference, she would have attended.

Michael Swan makes the same observation in his Practical English Usage.

Sometimes a simple past tense is used with if where a past perfect would be normal. This is more common in American English.

If I knew you were coming I'd have baked a cake.

If I had the money with me I would have bought you one.

If I didn't have my walking boots on I think I would have really hurt my foot.

An odd example or two can be found in the British National Corpus as well.

I couldn't have it done cos of work but I'd love to have it done. If I wasn't at work I'd have it done. (conversation)

Bloody hell! I came down here to try and find him. If I knew where he was I wouldn't have come. (fiction)

So, while it's not standard and no authorities endorse its use in serious prose, it does occur in informal contexts, and so would probably be best classed as colloquial usage.