The title of page 25 of the Patients Guide is "Foods that may affect mucus production" - that does not mean it will happen in every case - as @liz440 reported, dairy products don't affect her mucus, and in that she agrees with Dr Pamela McShane in her airway clearance webinar
( https://www.youtube.com/watch?v=VEYK67nld_o)

The original list , "30 Foods That Cause And Reduce Mucus Production" ("https://lunginstitute.com/foods-that-cause-and-kill-mucus/) refers you to an article called "The Anti-mucus Dirt"
(https://lunginstitute.com/anti-mucus-diet/)

Here is where life gets interesting!
The first list says PINEAPPLE is a food that may reduce mucus production.
The second article, on the same website says "Having increased histamine levels can cause your body to make more mucus. For example, bananas, strawberries, PINEAPPLE, papaya, eggs, and chocolate may increase histamine levels."
Even within one website, the experts don't necessarily agree.

So we need to be very careful when making any blanket recommendations - every body is different - like Liz found and I have found, dairy isn't a trigger for us - so we eat it.

Also, many times, I believe people don't differentiate between mucus production in the lungs and mucus expectoration. The mucus is there - if coffee helps us get it out, great. But the average person doesn't want more mucus to come out - they expect their lungs to take care of it silently.