This summary is not the rule. The rule text controls.
Once both sides have filed their initial court papers (like the complaint and the answer), either side can ask the judge to decide the case right then based on those papers alone. This is called a motion for judgment on the pleadings. The idea is that sometimes the papers already filed show clearly who should win, so there's no need for a full trial. This motion has to be filed early enough that it won't hold up the trial schedule.
If someone brings in extra evidence or information that goes beyond what's in the original papers, and the judge decides to look at that extra material instead of ignoring it, then the rules change. At that point, the judge treats it as a different kind of request called a motion for summary judgment. This means the case gets handled under Rule 56 instead, which has its own set of steps.
This matters because both sides get more protection when outside evidence is involved. Everyone must get a fair chance to bring in their own evidence and arguments before the judge makes a final call. So if you find yourself in this situation, you won't be caught off guard. Both you and the other side get the same opportunity to present a full case before the judge rules.