Rev limit mod cheat glitch Xbox

Playing in an a class lobby last night and noticed a brz with a 6.5 speed doing well over 200+ mph and accelerating at an unreal speed. Thought it was just a straight line rocket but he was doing well in the turns as well. I decided to spectate him next race to get a better look at the car. It then became very obvious that something wasn’t right (I am not sure how to share the video I saved of him but I have it saved on my Xbox) as he hit the rev limiter in 4th gear after a second or so of banging off the rev limiter rpms max out stop bouncing and his car then accelerates like a rocket jumping about 50 mph or so then hits 5th gear, rpms don’t drop but the speed is well over 200 mph in no time. His Xbox gamer tag is [Mod redacted - D]. Has anyone else seen this before? Is he cheating? Exploiting a glitch? Mod? What the heck is going on here? If you can clue me in or just wanna see the video send me a message on Xbox (Jaredz11) and I’ll send it to you

He was using a brz, v8 swap, not sure what else he did. His number speed 6.5 hand 5.1 accel 8.2 brake 4.9. A class build

When I messaged him asking him about the car. I also sent him the video. He stated my internet is bad and what’s my point lol… really…

Thanks in advance for any help regarding this issue. Let’s keep it clean and fair ladies and gentleman