He didn't improve the clock design or function. Its doesn't take any skill to attach clock guts to another case. So a hoax is the most plausible reason to jury-rig clock wires and electronic parts into another case and take it to a public school.
Whether he improved the design is in the eye of the beholder. I'm sure there are plenty of 14 year olds who would rather have a pencil case clock instead of an old factory issue one. Also, repurposing old items by installing electronics into them is "in" nowadays. When they're done well, people will pay good money for a fun and quirky case mod. For example, consider
case of bass. It's more polished work than Ahmed did, but it's the same kind of repurposing and reconfiguration.
It doesn't matter if you think it's pointless. Some people enjoy taking electronic components out of their factory issue housing and installing them into a different housing, and some people like case mods so much they'll pay for them. The case mod Ahmed did isn't strange or unheard of, and there's no reason to believe he meant to use it in a hoax.