The only problem with that wording is the word bonus. It otherwise says nothing about a base amount. So that implies 0. It really should just say 250MB like the other plan base amounts and no mention of bonus or autopay.
Some time ago though people did see two lines of 250mb stated. They had a case. I think some got it too. The company fixed that in a hurry.
@Yummy - yes agreed, it helps with marketing the plan 'more attractive' in the list of offerings. But, you could take out the words 'with Autopay'.
I suppose these are templates plastered in many places that are not linked to one source. So, for someone to update the material, it is not as easy as to change it in one place, than everywhere else is automatic. This one-to-many relationship may not exist.