The large bomb found in the jungle is not a Tallboy as previously suggested, but a "Grand Slam", the successor to the Tallboy bomb. The key indicator is the overall size of the larger 22,000 pound bomb, and the aerofoil shape of the stabilizing fins, versus the relatively flat fins of the tallboy.
It's perfectly plausible that such a bomb could sympathetically detonate after 60 years in the jungle. The explosive filler is a cast RDX/TNT based explosive (torpex) which is more or less impervious to the elements. While it's entirely possible, and quite likely that the secondary booster explosives would have deteriorated, and indeed the very fact that the bomb did not explode when dropped would suggest that the fuses were damaged or misused, it's entirely possible that a very large container of torpex could be sympathetically detonated with a C4-based claymore. The implausible aspect of the bomb is that, indeed, they were only used in Germany, were extremely rare and expensive, and could only be dropped from a fairly specialized Lancaster bomber.