I hope it's ok to ask this question. There seem to be a lot of people who know their fruit here.

Last March I planted a red guava in my southern California garden. This week I picked my first crop. Just two pieces of fruit, but I'm really pleased with the size and quality.

They're not what I expected, though. These fruit are larger  (4" length), and the color is more yellowish than red. It leaves me wondering whether I got ahold of a misidentified tree. What do you think? Is this a red guava?

 

It's probably a seedling from a red guava tree that was cross pollinated with a white guava tree.  There are a lot of decent guavas out there.  Try and get one that is grown from a cutting because that is a true variety.  I recommend Ruby Supreme or Ruby x (from Exotica Nursery in Vista, CA).  The grafted varieties from LaVerne Nursery are also pretty good.  I like Mexican Cream from them but its a yellow skinned white guava.

That doesn't look like my red guavas. Mine are darker inside and out, and pinker inside.

As far as I know, red guava have pink flesh

Yes, I agree. Red Guavas have a dark pink inside.

What are the seeds like?  I can't see them clearly.  They should be rock hard, tan and 1-2mm maybe 3 in all directions.

Here are some what is called Red Guava. I lost my plant in pot. Forgot to bring it inside one very cold night. I miss it because it is not easily available here:

https://www.google.ca/search?q=ruby+supreme+red+guava&biw=1553&bih=779&tbm=isch&tbo=u&source=univ&sa=X&ved=0ahUKEwjLqv_7iPTKAhVHKx4KHWHRCWwQsAQIHg

I've seen many Guavas offered at nurseries that are started from seeds, they come close to their parents, but was mentioned this seems to have been crossed with a white guava. I really like Ruby supreme, Malaysian red, and Egyptian guava.