I assume that the bus normally fits under the bridge. Heavy recovery usually lifts the front axle a couple of feet up to clear the road for towing. Is that what made the bus over height? Finger of blame should be pretty straight if so.
As I said, the picture (really
from WalesOnline) shows the bus with a solid tow - but there's no way to know if that's how it got there or if it's being recovered.

Bus 342 is listed as a Scania N230UD Omnicity double deck, so is almost certainly 4.38 m (14'5") high. The bridge is marked as 4.5 m (14'9"), so it ought to fit. The model has (as an option, I think) a Suspension Raise / Lower Facility (Ferry Lift). Other than that, something else not in the story or pictures must have made it higher, though not by very much.