Doping

So just wondered, have any of you trained with someone you seriously thought was doping? I train with someone who about 3-4 weeks ago, was of similar speed to myself, if not a bit slower on some things. This person is training for what I think is called an Ultraman - and they put in serious distance in all three disciplines every week. So, this person is already quite buff, not an ounce of fat on him/her, and I could tell s/he was just dragging, from all the excessive training s/he's been doing, when suddenly out of no where s/he's like 10 seconds faster in 100 repeats. S/he is super motivated, I'll grant him/her that, but in my experience that kind of improvement doesn't happen overnight like it has here. Not only that but s/he is now able to go like 7000, and maintain his/her tempo/speed/energy level to the end, when s/he was going only about 2500 in an average workout before. Thoughts?