Because it's extremely misleading. They're invoking the name of the Bhopal disaster even though they seem to know that the actual toxin released in that disaste

Because it's extremely misleading. They're invoking the name of the Bhopal disaster even though they seem to know that the actual toxin released in that disaster (methyl isocyanate) is not one of the chemicals on the NS train (or one of their products, as far as I know). Instead, they're talking about the chemicals "stored at" the Bhopal disaster, which may make the comment technically true (I don't know) but very very misleading since those chemicals had nothing to do with the mass death for which the incident is infamous.