The problem I see is that the air filter is mounted in a reverse flow configuration, and from the little information I could find about it using the filter in this direction isn't recommended.
For one, it makes it harder to clean (think of all the debris and bugs that'll get in there you'll have to somehow get back out).
For another, the oil needs to be added to the inside of the filter, rather than the outside of the filter in normal configuration.
One of the hits I got off google said that it's not recommended because the mesh expands in that flow direction, while in a normal configuration it compresses the mesh, allowing it to filter smaller particles.
It's easily remedied, just flip the can around so the filter is flowing the right way...provided the two ends are the same diameter and can be switched around.
You would have the additional option of being able to run it without the can for an open element, or slip the can back on for more protection, with just a few screws.
As for stuff sitting in the bottom of the can, the only way it can get INTO the can is by going through the air filter first in the way he has it set up.