They are totally different; however, a popular combination is guava paste with a strip of guava jelly down the middle
The jelly is a jelly; the paste is more or less a seriously dessicated finla product from a jam which has been really cooked down.
(That's my experience with the making of both AND the eating of both.)
Side point: on bread with cream cheese, spiced meat, and vin ordinare, you got major human food!
As a child in Cuba, I used to have it for an afternoon snack on French bread with either cream cheese or Edam cheese. Yummy!