There are differences
It doesn’t seem to me that the ELF and the ALF should always be spoken of in the same breath. The Animal Liberation Front is decades old and well-established in over 20 countries.
The Earth Liberation Front didn’t really appear on the radar until 1998, when a Vail ski resort was torched. There are questions about the communique in which ELF claimed responsibility. There are questions about the authenticity of ELF website. There are questions about whether the ELF exists as an organization in any ontologically robust sense.
In general, the animal-rights movement has a much longer and more storied history of violent direct action than the environmental movement. Lumping them together as one amorphous threat is driven as much by the political needs of the powers-that-be as by events on the ground.