The difference is St.Mirren were a decent team that year until the final game.
We lost 3-0 to Hearts twice, 3-0 to Hibs, 5-0 to Dundee United and 3-0 to Rangers that season. We lost 2-0 against the Bankies at Love Street earlier in the season.
We, and Hearts, have since gone on to lose to Celtic by crushing margins on many, many occasions.
There was absolutely nothing out of the ordinary about us losing to Celtic by that margin, when we had nothing to play for and they were going for the title. The only team responsible for Hearts blowing the title was Hearts.