I'm not sure it's a fundamental mistake. To make a counter-argument, if one travels back to some point in time, but can't remember (or don't know[0]) exactly when a major event happened, one might query it, to see if/when it has happened. Or one might query it because one is mistaken about when it happened. In either case, one might expect to see queries about things in advance of their occurrence. So while this particular work certainly doesn't rule out time travel, I don't think it's fundamentally flawed. Perhaps overly optimistic though.

[0] One might presume historical records are somewhat corruptible, and therefore someone from the future might not have perfect knowledge of when major events in the past actually occurred.