The way they achieved their goal was misguided but what you've described skips over large parts of the problem. Why would the server time and phone time be in sync?
It doesn't say anything about synchronisation between phone and server.
EDIT: In fact it is easier to implement it this way than using NTP. I've implemented something similar and I found it easier to add an API endpoint that returns time() than to ship an NTP client...
And you don't care whether the time on the server is running accurately if you're just using it to generate tokens which are checked against the time on the server. It just needs to be consistent, it could be an arbitrary counter and would still work fine as long as it counted up reliably at consistent intervals.