It's going to be up to your DM
This is definitely an edge-case - and even moreso because it's language used in Unearthed Arcana which Jeremy Crawford has stated that:
Unearthed Arcana material isn't tuned for multiclassing. We make a class/subclass multiclass-ready if it's going to become official.
Odd interactions like your question are bound to come up and will likely be dependent on tables as to how to adjudicate if multiclassing is pursued.
A reasonable approach
Having said that, it does seem like the two abilities should interact. The requirement for the curse is movement due to casting a spell, which is exactly what is happening with Eldritch Blast with Repelling Blast.
Your DM may initially allow it because of...logic :) But table experience may determine if the combo is overpowered or not. If so, don't be discouraged if they want to roll back the allowance and bar the interaction.
Multiple Blasts Concern
As Ben Barden pointed out, EB provides more than one blast. No other sorcerer cantrip that delivers cold, lightning, or forced movement does this. This is another interaction unplanned with the UA multiclassing.
Once again, it's up to the DM how they want to handle the curse application here. But given a successful series of hits could then push the target back in multiples of 15, this suggests a problem with the interaction and a reason not to allow it. However, if they decide "that's awesome!" and it works for them and the table - then allowing it is reasonable as well :)