The tick was most likely killed by the frontline. With frontline, it is spread over the body via the oils on the skin. A flea, can crawl around and come in contact with enough to kill it, where a tick pretty much has to attach itself. With or without frontline, I highly suggest keeping the dog current on it's lyme vax. More dogs contract lyme disease that we realize.
Breeding and Training Boykin Spaniels, a True American Gundog