Hello and thanks, it's all done by just me
The kind of damage you report is pretty common, and usually caused by an object between the tub and the drum. It's usually coins, but all sorts of things get stuck in there including nails and screws. It's possible for the damage to have happened when you used it last and you wouldn't necessarily notice it but when it happened there would have been some unsettling noises, so if you were in the same room and didn't hear anything maybe not.
Any damage as described would only happen on spin as the object was tossed around at speed. Therefore no water. However, once the hole has appeared in the outer drum, the next time the washer was used it should leak badly.
It's possible it happened as you suspect, though even if it did, it doesn't mean the person using it at the time is definitely to blame because objects like coins or anything else can get inside a washing machine and lay dormant for a long time only to suddenly appear and cause problems. If the washer has been making some intermittent strange noises on spin recently it could be the object rattling about prior to it getting punched through the drums. Even so, there isn't necessarily any "warning noises" either.
If the damage has been caused by a foreign object then the inner drum should be dinted inwards and the tear ought to be lifted upwards. In other words imagine something hitting it hard from the other side - it would punch the metal up.
Ultimately, unless the object can be found you can't know what it is. Bizarrely I've often been unable to find anything when I've visited such incidents but look under the washer and around it. You could also try disconnecting it from the mains electricity and having a look and feel around the chassis in the base which often has placed things can hide in.
There have been a number of incidents of Candy (and other brands) washing machines exploding because of a flaw in the inner drum where the welded seam comes undone during high spin and the metal drum explodes causing a lot of damage - washing machines exploding It doesn't sound anything like this of course but just in case the hole is on the seam I thought I'd mention it.
Finally, if the damage is caused by a foreign object it wont be covered by any guarantee although it's possible Hoover/Candy may still repair it for their fixed labour charge prices so it may be worth asking them what they'd charge under the circumstances - you can find their details here (although it's likely to be at least £100) - book washing machine repair
Finally, if you have home contents insurance with accidental damage cover it might be worth making a claim.