That's interesting - I suppose it all turns on whether "because they felt like it" can be translated into an "ideological cause". Does it have to be a cause shared by others?
I'd imagine if you asked most people for their definition of terrorism, they would place most weight on (b). The act of placing a bomb onto a train is clearly intended to intimidate to the public at large, irrespective of motive.
The Terrorism Act definition of terrorism is very interesting. It has been observed that it generally includes war, which is why we can use our counter terrorism powers against parties we don't like in the Syrian conflict.
s. 1 (1) (b) doesn't actually have to be met in this case, as subsection 3 provides that something doesn't have to meet (1) (b) if the action involves the use of firearms or explosives, although I suppose there is an argument that if the explosives only deflagrated, and were only capable of deflagration not detonation, they aren't explosives.