"Same tick" is a misnomer for a few reasons. First of all, games use UDP, which is basically a "fire and forget" protocol (which means packets get dropped routinely). Second of all, realtime games use some interpolation/prediction to make up for latency (and aforementioned dropped packets).

So it's sort of a "relativistic" temporal system, not a linear "oh now you're at t=1, now you're at t=2" kind of timeline. And there's all kinds of complicated ways you create concensus between multiple clients, between server and clients, etc. (A lot of this remains an active research area.)