Lemmy isn't one big place like Reddit is, it's a bunch of different services that connect with each other. The rules of what are and are not allowed varies instance to instance, and some instances block others entirely ("defederate") so if your instance does not allow porn, they likely defederated with instances that do. Either way, if you use the subscribed feed you shouldn't see things outside of the communities you've subscribed to, and communities also have their own rules (usually more specific than the overall instance rules, same as a subreddit's rules vs. reddit's sitewide rules).

I never said to check them. My bad for not saying not to, though.