I'd like to add some interesting points I've read from the first source

1. About Hasdrubal's guide who "betrayed" him, according historynet.com:

The Metaurus was in flood, probably from spring rains and snow melt, and Hasdrubal was trapped on the south shore, unable to ford the river. The ancient historians say he was deliberately led astray by his guides, but this is absurd. An army leaves a wide track, and surely Hasdrubal would have had no trouble finding his way back down a road he had already traversed. Also, what guide would be fearless enough to lead an army up against an unfordable river, with no means for the guides themselves to escape?

The unexpected barrier of an uncrossable river threw the Punic forces into disorder and confusion. Frantically, scouts searched up and down the riverbank for a place to cross, to no avail.
I'm not too sure, but that does make sense

2. And the messengers factor:

He sent messengers to his brother with strict instructions that, should they be in peril of capture, his letters be destroyed. The messengers traversed nearly the entire route in safety, but by mischance, when almost within reach of Hannibal, they were seized by a Roman detachment. It happened so swiftly that they were unable to destroy the letters in time. Thus Nero, rather than Hannibal, had in his hands the entire plan of the Punic campaign.
Which again made me wonder, if I get it right, why instead of trying to disperse the messengers and send them into different routes (in case one group get captured), he decided to send them all together instead?