Two possibilities come to mind. One is that the sequence of working/not working after your fuse replacement was coincidental, and in fact both units were damaged in succession by an external cause, such as severe mains transients or overvoltage. If you have a normal single-phase supply where everything runs from the same line and neutral in the consumer unit, then you would likely have noticed this problem in other ways e.g. other items damaged or flickering lights. Factors such as overhead supply and electrical storm would point towards this cause.
If, instead, the root cause was within the subwoofer, it might be that part of its circuitry at mains voltage has come into contact with the audio input. In equipment from reputable manufacturers this is extremely rare and usually indicates catastrophic internal damage. For example, if a product is dropped and the transformer breaks free inside due to the impact, it can drag mains-voltage wiring into contact with other parts. Because this is a dangerous scenario, equipment (especially class II / double insulated equipment) is designed specifically to minimise the chance of this happening. Other causes of such a fault might be overheating, incorrect manufacture, water ingress or incompetent prior repair.
What might then have happened is that after you replaced the fuse with the fault still present, when powered up while connected to the TV, current passed along the signal cable, through parts of the TV internal wiring and circuitry and to earth via some route (if the TV itself is not earthed, then through some other attached device or aerial cable etc.) If certain critical parts of the TV circuit, such as the power supply regulation circuit were damaged by the fault current from the subwoofer, then the TV's power supply may have malfunctioned and blown its own fuse. I.e. it might not have been the fault current from the subwoofer that directly blew the TV fuse but a chain-reaction from the damage.
Both items need autopsy by a competent electronic service technician to determine the sequence of events. If the subwoofer fault was due to faulty construction it should be reported to the manufacturer as other units may be affected and could pose a shock risk. If due to damage, then you are lucky the result was only a damaged TV.