Not quite. Even existing EVs (with some exceptions for older vehicles) will be charged the new basic VED rate of £195 when they are next due to renew (which could be in up to a year’s time).
What EV purchasers were trying to avoid was the expensive vehicle supplementary tax of £425/year for cars with a list price of over £40k, which EVs purchased/registered since the start of April are no longer exempt from.
As the vast majority of new EVs on the market fall into that price bracket (including all Teslas except the base tier Model 3), suddenly the yearly tax for most new EV purchases jumps from £195 to £620/year.
Assuming your Fiesta produces < 100g/km CO2, looks like you’ll now be paying £20/year (as it was manufactured before 2017, different rules apply) - could be worse!