Can you picture a piece of this plastic making its way further into the engine? If the mechanic is correct (find a picture of the insides of the intake and see if there really are baffels that can break off) the broken off pieces should at least be removed,maybe they can be “fished” out through another opening.
mshugna’s link does provide insight to the problem,did you read the posts? those guys are all over eachother because someone got their feelings hurt,so common with internet forums.