It doesn't matter if Ed knows more or less than the villagers about foraging, he is capitalizing on the idea that foraging is a way to supplement their food situation. The idea of foraging came from the memories of his previous life and it was something that those around him had not been successful with. In the storyline, Miinya states that their neighbor got sick from foraging (eating grass) and she didn't want to get sick. How Ed is different than his neighbors (besides being reincarnated) is that he has a unique skill called "appraisal" which allows him to identify the edible plants.
I feel that it is too early in the Manga to decide if he uses the knowledge from his previous life in a believable way. I think if I found myself in a similar situation and I had an appraisal skill I would have also tried my hand at foraging for food if I was poor and on an Iruka bean diet.
I'm not sure that the world-building is poorly made as we are only in the 1st chapter. So far what we have learned about this world is that:
8 years ago a city collapsed (we don't know the circumstances of why), but after the collapse, the surviving citizens moved to the outskirts of Tyre City forming the current slums now called Laniellda. Between Tyre City and Laniellda:
-There is a stark contrast between the buildings in the slums (wood makeshift houses) and Tyre City (Houses look to be made of wood and bricks).
-The roads in the slums are made of mud while in the city they appear to be made of cobblestone or brick.
-The City has guards and I haven't seen any in the slums.
-There is a store to sell Iruka beans and potions to the slum children for three coppers.
Note: If there is a Guild Hall, Town Hall, Library, or School where common knowledge can be shared we haven't seen or heard about that yet. We have also not been given an overview map of the area.
The citizens of Tyre City seem to give the slum children day jobs and allow them to work for a few copper coins, but not all the citizens of Tyre City are ok with hiring the children from the slums.
-The citizens of the slums wish to return to their former city.
-In the slums, there is a doctor (Miinyas Mom).
-Ed and Miinya were born in the slums.
-Ed lives with his Aunt and Uncle who are Miinya's mom and Dad.
-Black hair may also be a problem in Tyre City (Ed has black hair).
-The citizens in the slum are dressed appropriately (have worn out clothes or tattered clothes) for living in the slums while those in Tyre City are dressed in fairly nice attire probably significant to their jobs or social standing.
Note: Currently we haven't been told why the citizens of the collapsed city live in the slums instead of being absorbed into Tyre City. Possible reasons are:
-Accepting the refugees may be a strain on already limited resources
-Accepting the refugees could put a strain on local infrastructure and housing
-Accepting the refugees could harm the local economy and job security of its residents
-Accepting the refugees could cause geopolitical problems with surrounding countries or cities
-Accepting the refugees could fuel xenophobic attitudes and discrimination
-The refugees refuse to join Tyre City because they hope to return home someday
-The refugees refuse to join Tyre City because they feel that they would be treated unfairly
