Other mistake: When Tiara hands Sharpay the bag with the latte you can see that there is nothing in the bag, especially at the end of the scene when Sharpay tosses the bag behind her back. It would have spilled if there really was a latte in there.
Other mistake: In the scene where Ryan joins Kelsi for early-morning rehearsal, Ryan sits at the piano and starts playing "Just Wanna Be With You." However, the sheet music only shows the melody, not the actual music, and this is the first time Ryan has seen the song, so he has no possible way of knowing how to play it.
Other mistake: At the graduation, Johnny is shown graduating despite being in a different graduating class.
Answer: I think that they are just props. The owner of those jerseys has no relevence to the plot.. They might just be randomly picked names.