Hello Ishan
When the sync rule is enabled, the route will not be installed in the routing table unless the IGP being used has learned about it.
It is not looking for the route in the routing table, since it will never be there because this is a condition for installing a route into the routing table. It will only be installed if this condition is met.
What the sync rule does is cause the router to first check if the route is “known” by an IGP. What this means is it looks in the topology table in the case of EIGRP, or the OSPF Link State Database to see if the IGP has a record of this route.
I hope this has been helpful!
Laz