Lovely things African Dwarfs are! They can be a bit tricky to keep in a community tank, I typically recommend that people new to their ways keep them in a species-only setup until they become more familiar with their behaviors and needs - people often seem to expect that the needs of a frog are the same as those of their fish - but they're an entirely different amazing animal!
That said. . . it sounds like your frog is pretty normal ^.^
ADF don't see very well at all. Because of this, they often go into what we call a 'zen state,' where they freeze for periods of time in order to detect vibrations in the water. These vibrations help the frogs to 'see' where other creatures are in the water, and allow them to detect the location of potential predators as well as food sources. Unfortunately for them, we don't often feed ADF with live foods in our tanks. This puts them at a distinct disadvantage, as they are then forced to rely on their sense of smell to find food. Obviously, they aren't generally amazing at this. . . food landing on their heads and disregarded is very common with these guys, they will also 'pounce' in a fairly broad area searching for the food that they smell, oftentimes coming up with nothing while sitting on the food they're searching for! *sigh* In a speceis-only setup, this is all well and good. Provided they have sand, the food will stay on top, and they'll find it. . . eventually. In a community tank, there are greedy fish to contend with, and the food will typically be all gone before the poor frog ever realizes that it exists!
It is very important to target feed any frog being kept in a community tank, as they will starve to death with food all around them. . .
A bit more about food. . . flakes do not contain what a frog needs to survive. There are specific pellets made by Reptomin (what you have?) that are made for these critters, and contain the higher-protein foods that they need. Unfortunately, not ALL frogs seem to see these as food - I've given up on the pellets, as my babies just . . . won't eat them! The best way to feed a frog, in my experience, is with defrosted wet-frozen foods - brine shrimp, blood worm, Mysis. . . you can even give them shredded bits of raw Tilapia fillet (they love the stuff!) Variety is always best, but avoid freeze-dried foods as they can cause bloat.
ADF are easily trained to take food from a turkey baster, tweezers, or fingertips, and will even learn to go to a specific area at feeding time - which makes things easier on everyone. A young frog will need to be fed daily, but an adult can be fed every other or even every third day without harm. They ARE very small, so you'll have to be very careful not to over-feed them or they can become ill - two or three bites is all they really need. . .
Wonderful image - you just made my froggy day! THIS behavior is of no concern with these guys *giggle*. . .when they go into their Zen mode, they will just allow themselves to go where the water takes them, which often includes drifting, falling over, being pushed aside by fish. . . silly little things. . . you've got a CUTIE there! How long have you had him, and how long since he ate? He doesn't seem overly thin to me. . .yet.
I hope this helps a bit? Let me know if you have any other questions, and WELCOME to TFK!!!