Exploding smartphones are nothing new, especially when it comes to Samsung. Infamously, the South Korean company recalled all Galaxy Note 7 units because of a battery-related overheating issue, although it later went onto to sell a modified version called the Galaxy Note Fan Edition. Since then, no widescale overheating issue has affected Samsung handsets, although there have been a few isolated cases.
More recently, Bangalore Mirror reported of the woes of one Galaxy S7 Edge, which reportedly exploded while not in use. According to the account given by the owner of the three-year-old handset, which was purchased in December 2016, the device caught fire after becoming hot to the touch. Apparently, the device was not connected to the mains at the time.
Samsung since responded by denying any responsibility for the incident, blaming "an external fire / heat source" for the damage incurred. The family are reported to be considering legal action against the company, who claim that the device had only ever been charged with a first-party charger and USB cable.
It appears that the incident occurred late last year, based on what we can deduce from the report on Bangalore Mirror. While a report of an exploding Samsung smartphone this close to a Galaxy UNPACKED event is unfortunate, it is not necessarily a "potential PR disaster" as it has been described. For one, not all the facts of the matter are known, nor is it a recent device. Linking this to the release of the Galaxy S20 series certainly seems unfair and misleading, at any rate.