What’s the difference between single source attribution and multi-touch attribution models?

There is no difference between single source attribution and multi-touch attribution models.
Single source attribution models assign each contributing channel a slice of credit for the final conversion, while multi-touch attribution models only give credit to the channel most responsible for the final conversion.
Single source attribution models assign credit to one touch point along the buyer’s while multi-touch attribution gives each contributing channel a slice of credit for the final conversion.
Single source attribution reporting was invented first. Once technology advanced, multi-source attribution became the new method of reporting.