Every menagerie battle is different in terms of possible experience gains. Also, the level of the carry pet makes a difference as well.
Some quick menagerie experience rules I have found:
1. If you click on the post or a tamer (squirt for example), the battle gives 3.0x more EXP. Single pets that you click on directly do not have this bonus (Beakinator, Quintessence, Eleanor, etc.), so they will give 3.0x less exp.
2. Number of pets, just like in every other pet battle, affects the amount of points: 1x for 1 enemy, 2x for 2 enemies, and 2.5x for 3 enemies
3. If you want details on why, check my guide out, however either way: level of pets affects EXP gains as well. A level 10 or 11 pet will net way more EXP than any other levels. A level 24 pet gains the least.
If Stitches Jr. was a "post" activated battle, he'll get the 3x bonus while the Beakinator, who is not activated by the post, will not. Both are single pet battles, so the get 1x multi pet bonus.
I'm working on getting the menagerie data into my guide but atm you can only do each menagerie battle on a single day so if I am busy with RL that day, I don't get to data collection. I'll eventually have all this listed out with charts.
TLDR: Nothing out of the ordinary aside from the post being considered a tamer and there not being a post today.
Carry Pet Experience Reference Guide: