Tank issue

We live in 4 in a block 1950s house. Our cold water tank is housed in upstairs loft. Our hot water is in our own cupboard. Last week water flooded down walls from upstairs. Upstairs is blaming our tank ballcock being faulty. Is this Possible? Would water not have came from overflow outside, rather than flooded the walls? They got someone to fix it but he was not a fully qualified plumber and is unsure what house the faulty tank belonged to?