This summary is not the rule. The rule text controls.
If you're sued in small claims court and want to file a counterclaim that's unrelated to the original claim, there's a dollar limit you need to know about. Small claims court can only handle cases up to a certain amount of money. If your counterclaim is for more money than that limit allows, and it's about a completely different issue than what the plaintiff sued you for, you have a problem.
In this situation, both sides would need to agree to let the small claims court handle the case anyway, even though the counterclaim is too large. If both people don't agree to this, the judge has to dismiss the counterclaim. This means the counterclaim gets thrown out of small claims court, but it's dismissed "without prejudice." That's a legal term meaning you're not blocked from filing that counterclaim again. You can still take it to a different court that has the authority to handle larger claims.
Basically, this rule keeps small claims court focused on cases within its size limits. If you have a bigger, unrelated claim against someone who sued you, you'll likely need to pursue it separately in a court designed for larger cases.