The clause is:

If we make changes to this Agreement, you are not required to accept the amended Agreement, and this Agreement will continue to govern your use of any Licensed Technology you already have access to. However, if we make changes to this Agreement, you will not be allowed to access certain Epic services or download the Licensed Technology unless you have accepted the amended Agreement.

My understanding is this is fundamentally different to the Unity clause you're pointing out.

Another thing is that Unreal is ~~open source~~ source accessible. If there's a bug in 5.0 that is resolved in 5.1 but you don't want to accept the amended terms for 5.1, it's possible to fix the bug and build the engine yourself. In the event of a significant change like the one with Unity, I imagine some dev group would just fork it and maintain it themselves.