It’s not a direct cause and effect between better reading and propaganda resilience, it’s an enabler hence gets reflected as “probability of”, not as a certainty.

The more effective you are at taking in information and gaining understanding through reading, if you actually use it often, the more you know (both in terms of contextual knowlege around various subjects and other things you read on that subject hence have references to compare new information about it) so the more resilient you are to propaganda (for example: some things are only obviously illogical if you know enough about the context to see that they can’t happen as a piece of propaganda is trying to convince you they did).

Being good at reading doesn’t make people resilient to propaganda directly, it makes it more likely that they are resilient to propaganda because it’s easier for them to acquire broader and deeper knowledge so many do, whilst many who would otherwise tend to seek broader knowledge give up because their level of reading makes it a much harder task (for the latter reading is a barrier more than an enabler).

This is also why reading level isn’t an elitist thing: bright curious people no matter their origin will go much farther if they have better tools to acquire knowledge and understand it, and the fastest most effective way to provide a lot of those tools to them is schooling, so if they don’t have them it’s probably not their fault.

PS: also and as a side note, to get to advanced levels in lots of occupations you need the capability to acquire lots of information, hence you need to know how to read at a good level (for example, for dealing with certain cars, a car mechanic will have to read technical manuals - they can acquire the knowledge for run-of-the-mil repairs from others, but for advanced, better paying work they have to be able to figure it out themselves and in the present day that will be by reading technical manuals). Sure, people can “function” with low reading skills (that’s such a low standard that both my grandmother and my grandfather could “function” as totally illiterate people), but low reading level makes it harder to prosper in the modern world because so much of the advanced stuff is “locked” behind complex texts which require fast reading with good reading comprehension to be “unlocked” in a reasonable time frame.