Hello @jhilahd,
I believe the +5 modifier is a hypothetical. The source is indeterminant and does not matter.
I think the phrasing is a bit off. Try this reading:
"Always compare the roll against the final, modified value of the Statistic. For example, if a Skill with a value of 6 receives a +5 modifier for a final value of 11, a die result of 11 now scores a critical, while a result of 6 (which would have been a critical without the modifier) now counts as a regular success."
Does that work for you?
Also, I hope your group turns around! Playing Pendragon is one of the best things in the world!