The food that Lum accidentally makes is tsukimi-dango, a type of dumpling the Japanese prepare for the Tsukimi (full-moon viewings) parties that take place in the fall. That fits the logical connection between Ataru eating the alien version of a snack consumed during the full moon, and him turning into a werewolf.
Ataru's Mother:
Oh why did this happen?
Ataru's Father:
Don't cry dear.
Ataru's Mother:
But our only son, on whose behalf we have endured so much hardship, has gone and become a raccoon-man! I can't show my face to the neighbors!
Ataru:
I'm not a raccoon! I'm a wolf-man!
Ataru's Father:
Really? You look more like a dog-man...
Japanese