The quote suggests that the drink itself was likely harmless and safe to consume. Despite this, the character anticipates potential health issues resulting from the cup, not the drink, indicating concern over the vessel or the situation rather than the beverage's safety.
"He would probably get pleurisy, quinsy and pox from the cup" humorously implies that the cup might be contaminated or risky, highlighting the character's fears or the peril in their environment. Overall, it emphasizes a blend of realism and humor about health risks during that era.