You're right I used the term interchangeably - AWS Lightsail would have been a good service comparison, and those do start at $3.50[0]. The $8 figure came from running the smallest Fargate task at .25cpu and 512mb, excluding the load balancer etc. [1]
It was announced that App Runner (today) allowed for smaller instances[2], and the price/mo for this instance would basically be 1/4th of the previous default. So ~$14 [3]