Yeah this is unfortunately a very common line of thinking. Restaurant workers get tired of people claiming allergies just because they don’t like something. And over time, they get lax with food safety practices, or even outright ignore them because they think the person is just faking it.
Even worse, some people will intentionally “test” allergies to see if the person is faking. Because they genuinely don’t believe the person, and want to prove they’re lying.
My buddy is deathly allergic to peanuts, and has had several reactions after explicitly clarifying with the server that there were no nuts in the food. And he actually ended up breaking up with a girl because her mom tested his allergy. She added peanut powder to some brownies she baked, then told him they were nut-free. He found out that his ex knew about it, (and didn’t warn him), which is what led to the breakup.