I don't expect the two events are related. There's nothing you can do at the CU to 'alter' how the laptop charger works - either it gets 230V between L&N in which case it charges the laptop, or it doesn't. Polarity doesn't matter. Inside the laptop, the 20V DC - or whatever the charger produces - is converted to various other voltages including 5V for the USB output. So even a malfunctioning laptop charger would, as you say, normally fry the laptop innards first, before affecting anything plugged into the USB ports.
The only really obscure and nasty scenario I can invent to connect the two is that the final circuit that the charger was plugged into had its CPC connected to line at the CU, making the laptop chassis (and probably everything else in the room) live. Then somehow the output side of the bike lamp charger contacted real earth potential and the fault current passed through the laptop charger and laptop DC ground without visible harm but fried the final link in the chain.
Other than this almost-inconceivable occurrence, it's just coincidence.
It's hard to get enough power out of a USB port to do real damage, even at 2A it's 10W, half a soldering iron's worth of heat. But if something on the output side shorts, the lamp battery might discharge back into the short and even a small LiIon can pack a punch and burn things out sharpish. Also, some of these products are not made of properly self-extinguishing plastics so once something gets too hot, the whole casing bursts into flame.
I would be interested to see a close-up of the PCB from inside the charger. I see a lot of blown-up power electronics and can often reconstruct the chain of events.
