The Vietnam mine incident was part solar storm, and part incompetence.
I'll leave it to the reader to research 'telluric currents', which is how the energy got transferred to the mines. The incompetence part comes from ignoring standard procedures and safeguards when laying the minefield. The US and other major military powers of the world have long and detailed empirical examples of those threats. Too many of them in the wrong proximity to each other leaves them vulnerable to such a spiked telluric charge. Since WW1 it's been known, which is why such incidents are so rare.
If anyone hopes to understand why the earth is threatened by solar activities, they need to research four things.
1. Telluric currents
2. Faraday's Law of Induction
3. The methods of energy transfer from the sun (flare, wind, CME, etc)
4. The earth's magnetosphere