Dean Shiels put the visitors ahead within one minute of the second half starting and Nicky Law had a goal ruled out for offside before 18-year-old defender Lewis Martin headed home an equaliser.
Despite two surprise dropped points against a home side that made 11 changes in anticipation of their play-off duties in midweek, McCoist believed it was a day to celebrate.
"Initially right after the game you are disappointed but a minute later when you think about 33 wins out of 36 with three draws I would have to say it is fantastic," said the manager.
"Obviously we wanted to win the game but we wanted to get through the entire league season undefeated and I have just said to the boys that the entire staff are unbelievably proud of them.
"The most important thing from our point of view was that we got through the game without defeat.
"They probably won't realise it tonight or tomorrow but they will certainly look back a few years down the line and be extremely proud of themselves and so they should be.
"For me it is a fantastic achievement. You can only beat the opposition that is put in front of you - everyone tells you that. I think the fact we have only had three draws out of 36 tells you a lot as well.
"Obviously in one or two games you need to carry a bit of fortune and we have done that along the way but if somebody had said at the start of the season that we would go through the entire league campaign undefeated then we certainly would not have thought that would be possible.
"I will let others make their own minds up on what level of achievement it is, but without doubt it is an achievement."
Dunfermline boss Jim Jefferies was delighted with the performance put in by his young players against a near full-strength Rangers side.
He said: "Rangers played a very, very strong side - probably their strongest that was available to them - so I think looking at the two team sheets you could easily have thought 'this is going to be one of those long days'.
"But every single man out there was magnificent, they stuck to the shape that we asked them to play. Rangers had most of the possession but they could not really do anything with it and were not really hurting us.
"There were nine players out there who came through our youth system - that speaks volumes for what we are doing behind the scenes here.
"The players did themselves and the club proud with that performance."