IDK iof there is much to discuss with Blue's Pidgeot there (maybe your Pokemon just had a good defense stat?)
Happiness is affected by winning battles, walking, some items (e.g. certain berries) and haircuts. However this does not affect if two Pokemon will like each other or breed.
Pokemon will only breed if in the same egg group or with a Ditto (look on serebii, bulbapedia, etc to see what is in what). How much they 'like' each other determines the chance they will make an egg every certain amount of steps. Different species and same Trainer ID will not like each other much and hence have the lowest chance of making an egg (e.g Pidgey and Ditto both caught by you). Same Pokemon species and caught by you, OR different species, diffrent trainer IDs hav a better chance (iirc ~ 50% every 256 steps?) and same species, different ID have the best chance.
Please ask questions in the Help thread sticky at the top of the section next time. Closed.