The reminisces of the Yorkshiremen being exaggerated IS the point, so they got ridiculous in stages until those 2 went way over-the-top. (I thought the final topper ended pretty humorously because I didn't think even a wild exaggeration would go that far.)
The blancmange that played Tennis was from the planet Skyron in the Andromeda Galaxy. Perhaps there's tennis-playing, human-eating blancmanges there. I've seen speculative discussions more ridiculous than whether African swallows could carry coconuts whether gripped by the husk or in tandem, whether or not they're non-migratory. Those were all where the skit was going. I thought the MSG thing was a script error. Although I like DannyBeans' suggestion that they were hypocrites or deliberately inconsistent (per the script, but thinking they were consistent) and clueless about it.
I'm leery of calling something "natural" just because small amounts could potentially be found in nature. I don't think of High Fructose Corn Syrup as natural even if they extract it from corn. You wouldn't just encounter a bunch of it in the wild. I think that's more advertising/creative misrepresentation than being correct. (Even if they DID get the MSG from processing seaweed.)
(To me, it's a little like YET ANOTHER writer claiming humans use 10% of their brains-and that from the mouth of someone who knows medicine, psychology or biology. From someone we know is a liar or a fool, I'm ok with the claim because I know how far to trust them.)