Learn English – Difference between “flavourful” and “flavoursome”

Per OP's revision, it's from Family Guy, Series 9 Episode 9, titled "And I'm Joyce Kinney" where Lois makes a porno and shows it in church. The word porno in the sense of a single instance of porn (i.e. - a video, in this case) occurs repeatedly in the episoide - for example, Brian says "Lois! You were in a porno?".

Seth Macfarlane (creator of both Family Guy and American Dad) has an excellent ear for language usage, and I have the distinct impression he likes to raise little quirks like this. Probably with all the success he's having, he actually has people around him actively seeking out such tidbits for him to consider using in his cartoons.

Digressing slightly, I think there's a reason why "quirks of English language" occur more often on "adult cartoons" than we might otherwise expect. Native speakers subconsciously "know" much more about usage than they're normally consciously aware of. When you see something like OP's example, there's a strong tendency to think "Yeah! I know that too! I'm smarter than I thought!". You end up feeling good about yourself when you watch it, so you're up for more of the same.

Regarding the specifics of "accepted usage", Lois is correct that "a porn" is, well, weird, - "porn" is an uncountable mass noun ("The Church disapproves of porn"), or an adjective ("Lois made a porn video"). Sometimes "porno" is used as an adjective too, but never a mass noun - usually, it's a countable noun ("Brian made several pornos", each a single item of pornography). A porno is normally video - I've never heard it used of pictures, writing, audio recordings, etc.

The terms technically resemble each other, but in my experience, "sensuous" is a less excitable term and refers to information taken in through the senses; whereas "sensual" is more provocative, even suggestive. The latter would be more pleasurable as a rule. Here's a note from my computer dictionary (New Oxford American):

usage: The words sensual and sensuous are frequently used interchangeably to mean ‘gratifying the senses,’ especially in a sexual sense. Strictly speaking, this goes against a traditional distinction, by which sensuous is a more neutral term, meaning ‘relating to the senses rather than the intellect’ ( swimming is a beautiful, sensuous experience), while sensual relates to gratification of the senses, especially sexually ( a sensual massage). In fact, the word sensuous is thought to have been invented by John Milton (1641) in a deliberate attempt to avoid the sexual overtones of sensual. In practice, the connotations are such that it is difficult to use sensuous in Milton's sense. While traditionalists struggle to maintain a distinction, the evidence suggests that the neutral use of sensuous is rare in modern English. If a neutral use is intended, it is advisable to use alternative wording.

Perhaps, "Our day at the spa was exceedingly sensuous" vs "Her whisper in my ear was so sensual I could hardly take a breath."